Day trip to Bath from London.....

We went on a Sunday in December because the ticket prices were lower than during the work week, especially during the rush hours. You can check prices at: https://www.gwr.com/plan-journey

In spite of train fares being lower, I'd probably go on the Monday or Tuesday. Weekends are really busy in Bath with the people doing a 2 or 3-day getaways and hen weekends so I'd wait until they cleared out. The Monday would be good unless it's some kind of Bank Holiday!

Roman Baths are open every day as is the Fashion Museum. I don't recommend the Jane Austen Centre as I found it overpriced for a location where she did not live and which has nothing original of hers.

They can check the Bath tourist office site to see if anything they want to see is closed.

https://visitbath.co.uk/

On work days, the Off Peak rates are available for travel after 9:30 a.m., so you could depart London Paddington at 9:32 to arrive Bath Spa at 10:52. That might be good timing if you're eating breakfast at your hotel. If they're locking in tickets and departure times up to 3 months ahead, then Advance rates can cheaper than the Off Peak rates, regardless of time of day, and would ease the cost if you want to get an earlier start.

Most of Bath sightseeing is open daily in May/June (whether crowded or not), but I notice these couple of things that aren't (based on RS England, 8th Edition, starting from page 410): Museum of Bath Architecture closed Mondays, American Museum closed Mondays, George Bayntun Bindery Bookshop closed Sat-Sun, Bath Boating Station rentals closed Mon-Tues. Anything with shorter Sunday hours (such as churches and shops) are also discussed in the book, but variances are pretty small.

Concur that the Jane Austen ctr is a bit pricey but nice neighborhood for walking and you can go into the gift shop for free.

Fashion Museum well done and worth the time of that is their interests. Our tour had lunch in the Pump Room (very nice) and then we toured the Roman Baths below it with self guide/ audio boxes. So much to see but crowded.

I'd go on one of the weekdays.

What about a tour? I mentioned this to them because I figure it would relieve some of the stress involving transportation.
Thanks

If they go for a tour, try to do one that just goes to Bath not a bunch of other stops.

TBH, the transportation out to Bath is very easy. I’ve never lived where there is public transportation so I’m basing my statement on how easy it is for me, lol!! Definitely look at purchasing train tickets as soon as they go on sale for the least expensive options.

Not sure where they are staying in London, but I didn’t find the trip stressful. Catch the train from Paddington and when you step off in Bath, it’s a direct walk into town. There’s a good description of leaving the station in the Rick Steves guidebook. I traveled on a Monday. As far as I could tell, all the sites were open.

I went into the Abbey, having seen the Roman baths on a prior trip, walked the side shopping streets a bit, walked to the costume museum, had tea at the Jane Austen Centre (did not tour the Centre, though), walked to the Royal Crescent, headed back down the hill, stopped at Marks & Spencer, then caught the train back to London. A full day and very enjoyable.

Many shops are shut on Sundays. The ‘cheap’ advance fares for the dates you are thinking about are not yet loaded to the system. I have just checked for Sun 10 May & Tuesday 12th May and the advance fares are indeed loaded. On the Sunday, you should be able to advance purchase a specific train for £16 per person each way (£32). For Tuesday 11th May, I see that the 9.02 from PAD (are.Bath at 10,24) is priced at £21.50 & I can find a similar price for a single back to London (£43 total per person). So, advice is to wait a few days for the lower prices to get loaded before making your booking. You will need your debit card and be given a booking number - which you should take with you. (You need to nab the advance fares near when loaded as the prices tend to go up with demand).

The trains are much faster than going by road and most of the main sights in Bath are all walkable from the station.
You will be travelling on these trains (green ones):>https://www.youtube.com/watch?v=CGXboGzZiXI
View from inside the train:>https://www.youtube.com/watch?v=idPuWuBkFTg

Picking up on the comment about opening times made by Laura the Museum of Bath Architecture is actually open on Mondays 1-5 . Check here.

https://museumofbatharchitecture.org.uk/planning-your-visit/

Rail travel on Sundays can be affected by routine maintenance which is usually done then. This can alter timings and if sections of the line need to be closed, you may have a shuttle bus service instead. Given the choice, I would choose a weekday.

The latest day for which Advance tickets have been loaded into the system by GWR at time of writing is Friday 15 May.