Kyle, when figuring out drive times, you should add 20% to Google's drive time because of the roads. So, I think the drive from Pitlochry to Ullinish on Skye would be 5 hours. That is doable in one day, IMO. We were in Scotland in June, and one of our drives was about 5 hours. Pitlochry is a pleasant town. We stopped there for lunch one day.
Regarding how much time on Skye and how much time in Glen Coe, that's a difficult call. For me, anyways. Skyegirl can help you out more than me. But I will say that while I loved every place we visited in Scotland, Skye and Glen Coe were our favorites regarding scenery. The scenery is spectacular and stunning! I think 3 nights (which you have) should be the minimum for Skye. We had 4 nights, so 3 full days. We had 2 nights in Glen Coe so one full day. I wish we had an extra night.
I think your decision whether or not to do 3 nights Skye/2 nights Glen Coe OR 4 nights Skye/one night Glen Coe depends on if you think you will make stops along the way from Skye to Glen Coe, which is what we did, or will you drive directly to Glen Coe, and therefore, arrive earlier in the day than we did. And will you stop along the way from Glen Coe to Edinburgh, such as visiting Stirling Castle. Do you plan on doing some hiking/walking? In Glen Coe, our highlight was driving along the Glen Etive Road. The scenery is stunning although the rhododendrons won't be in bloom in October. But I assume you will have beautiful fall scenery. Glen Coe is a hikers/walkers paradise. If you only stay one night in Glen Coe, you could drive down the Glen Etive Road before you head to Edinburgh.
On Skye, we followed the On the Luce driving itinerary. It's a 3-day roadtrip, so requires a 4-night stay on Skye. Here is the link in case you are interested:
https://www.ontheluce.com/isle-of-skye-itinerary/
In Glen Coe, we stayed at the Glencoe Inn in Glencoe Village. There is another nice inn nearby - The Clachaig Inn.
https://www.crerarhotels.com/the-glencoe-inn/?utm_source=google&utm_medium=organic&utm_campaign=gmb
https://clachaig.com/
And we had lunch one day at the Old Inn in Carbost that Skyegirl recommends. Delicious meal overlooking the lake.
This is the link for the Glen Etive Road.
https://www.ontheluce.com/glen-etive-road-scotland/