Oban to Portree

I'm afraid you're going to find this is not practical--maybe not even possible--as a day trip by public transportation, if that's what you're hoping to do.

This is where I'd start: https://travelinescotland.com/.

Then I'd check any rail segments on https://www.nationalrail.co.uk/, because I've occasionally seen differences between the two websites for train legs, and I consider NationalRail the official source for rail info.

As you can see, it appears the trip will take at least 6 hours one way, with some connections along the way.

Even if you had a rental car at your disposal, ViaMichelin estimates the driving time (no stops, no traffic delays, no navigational errors, etc.) at over 3-1/2 hours each way.

You really don't have time. It's the best part of four hours by car. Public transport probably becomes six to seven hours.

There are plenty of great place between Oban and Portree worth visiting without wasting hours travelling

It's not quite clear if you are going from Portree to Oban, or the other way.
Instead of vague it can't be done and use the train, there are several previous threads on this.
There are two coaches a day on Scottish Citylink. Both are change in.Fort William.
Depart Portree at 0730, arrive in Oban at 1403, or at 1035, arrive 1923 with a long stop in Fort William, so the early coach is better.
Not a train or ferry in sight.

PS- I am assuming you are overnighting in Oban, not returning to Portree the same day.
The distance makes that unwise, if not actually impossible, as you would only get 2 hours in Oban, departing at 1557 and getting back to Portree at 2154

I fear this is intended to be a same-day roundtrip because Audrey is on a tour with a free day in Oban.

I live on Skye and have never been to Oban! That's because it's just not practical to do so and get back again in a day. And I have my own car and am used to driving on the roads here. There is no viable public transportation routing that would get you there and back in a day. And even if you were able to get to Portree what you would find is a small village that most visitors to Skye use simply as a base from which to explore the island. So I'd say this is not a good plan! Far better to explore Oban on your free day.

Jacqui (Skyegirl)

I'm just looking at Rick's recommendations for the free day in Oban- Day 5, and am surprised that there are so few options shown. Apart from Kerrera and Lismore not mentioned are the Slate Islands, Bonawe Iron Furnace, Duart Castle and Tobermory on Mull. Kilmartin Glen and Cruachan HEP station.
All easy and worthwhile days out by transit.
If more adventurous on certain days of the week there are even sightseeing flights from Oban Airport or even air/sea combinations to Coll, Tiree and even Colonsay.
You should be able to get to Inveraray Castle with ease.
There are a whole weeks worth of really good trips there, and that is far from a definitive list. There are several longer ferry trips you can do as well.

To get to Inveraray from Oban, one would probably need to take the 7:45 AM bus that arrives at 10:21. The next departure (at 9:20 AM) arrives at 1:46 PM, far too late to make anything earlier than the 7:52PM return bus practical. The latter is a great, direct bus, but it doesn't get back to Oban until 9:07 PM, which is rather late when you're on a tour and probably facing an early start-up time the next morning.

Rural buses in Scotland tend to run infrequently, so you need to check very, very carefully before committing to a trip. The somewhat unpredictable weather is a complicating factor. In Inveraray, for example, there's something of a walk (uncovered) from the bus stop to the castle.

The direct buses to Inveraray (of which the 0745 isn't) depart at 1030 and 1255 (a 75 minute journey), coming back at 1618 and 1952. This is the timetable from the operator- https://www.citylink.co.uk/media/dazl4dps/glasgow-oban-apr23.pdf

The times given above match with those in Traveline Scotland.

That's odd. I've just rechecked, and I see the 9:20 AM departure as taking 4 hr. 26 min., arriving in Inveraray at 1:46 PM. Then there's a 1:30 PM departure taking 2 hr. 56 min., arriving at 4:26 PM.

On the return, TravelineScotland is giving me a 1:56 PM departure taking 3 hr. 21 min., arriving back in Oban at 5:17 PM. Then the 2:12 PM departure is shown as taking 5 hr. 30 min., arriving at 7:42 PM.

I wonder whether this is one of those cases when the website doesn't deal well when you access it from a different time zone. I've been looking at dates in June, but for this last check, I used May 17.

Edited to add: I was using MS Edge as my browser.

My feeling is that we are trying to over sophisticate what was only a suggestion in the first place on a very, very easy journey. Too much 'checking' going on here. There is a perfectly clear 'paper' timetable. Why that can't be used I simply don't know.
I am unclear exactly what is going on here, but I think it is that traveline is over sophisticated.
There are 3 adjacent bus stops in Inveraray- on the ground all is crystal clear (no mistake is possible), but traveline seems to assume you mean one stop over another and trying to get the right stop in is proving hard, also I think it has a live link into the Citylink coach system and rejects journeys which are fully booked- a hypothesis, but not an unreasonable one, based on a whole series of checks covering many random days, which gives different answers each day. I have now spent several hours on what should have taken minutes.
The other issue is that Traveline will show a route I was trying to with-hold from you- the local bus routes to Lochgilphead and then on from Lochgilphead to Oban- I was with holding that from you because that is too complicated IMHO and too long a route, but of course traveline gives it.

If you look back a number of threads to another one on Fort William to Oban there was a prolonged and unhelpful slanging match where PM's were clearly flying behind the scenes. Again far too much 'checking' and far too much reliance on technology.
Half the slanging match there was about exact journey times and where buses left from. Again Traveline over complicated it by insisting you knew which bus stop was used in Oban, and starting your bus journey on a pedestrianised street in Fort William, from where you walked to the bus terminal! I had to get Citylink to amend their system (they had forgotten to add a summer timetable in), and e-mailed statements from both Citylink and West Coast Motors (the company who run both routes for Citylink) that the service ran, as no-one on this forum was interested in actual physical timetables and actual use of the bus, only in technology. That took a lot of my time which should not have had to be expended.
In this (Inveraray) case WCM website is again out of date. I am not wasting more time getting WCM to update their website.

In this case if you want to rely on technology, and not use a real life timetable, just forget I mentioned Inveraray- there are plenty of other options in Oban for that day, which are hopefully not in dispute.
The same problem also happened on a different enquiry in Falkirk where "technology" triumphed over actual physical real life facts.

thanks, isn31c. It's very helpful to know when a transportation website really shouldn't be used as the final source of schedule information. Other than a few rail-schedule issues, I had no trouble with TravelineScotland when I used it in 2019; perhaps I was lucky then.