Would you count the Sleeper?
The Chieftain arrives from Inverness at 20:06 and the Caledonian Sleeper leaves at 20:44. In terms of the last day of your ALR, this would have been a valid option until recent changes to Caledonian Sleeper ticket acceptance policy (now you have to have a ticket valid for both days of your journey). Basically, all stations served by the Chieftain North of Stirling would fall into this category (i.e. Gleneagles, Perth, Pitlochry, Kingussie, Aviemore).
Aberdeen is another one where you can't get a direct day return, although you can head North and catch the sleeper back. This also holds true for Stonehaven, Montrose and Arbroath, although you can go to Dundee and head back south from there on the same day.
Interestingly, although Glasgow is clearly possible in a day now, it currently has no direct services from London that provide a same-day return due to the WCML closure (although you can head South and back for the day on the once-daily VTEC service via the ECML).
Out of curiosity, how did you get back from Glasgow?