I've been thinking about Tony's route and how he might have changed his plans. If he realised part way into his journey that he had bitten off more than he could chew, his only way home was by rail and that meant he had to reach a railway station.
Once he left Fort William the first place he would have found a railway station, other than by returning to FW, was at Bridge of Orchy and the second was at Upper Tyndrum.
Bridge of Orchy
The station building at BoO has been turned into a bunkhouse, actually an independent hostel, for walkers on the West Highland Way, so he could have got accommodation there for the night. Presumably he didn't, so his other option was to use the waiting room, unless it was locked overnight, and take the first train out.
The last southbound train of the evening leaves at 20.48 or 21.35 (possibly depending on weekday or weekend schedules) and the first train of the morning is 09.07.
The station itself is unnmanned and has no facilities other than the waiting room (there is no CCTV), so the question is whether the waiting room is locked overnight, and if so when is it locked and unlocked and by whom, or is it left open all night as an emergency shelter for walkers?
AFAIK hostels, and some bunkhouses, are manned so in theory the warden at the bunkhouse could have locked and unlocked the waiting room, but did he or she do so?
https://www.thetrainline.com/train-times/bridge-of-orchy-to-glasgow-queen-street
Upper Tyndrum
This is also an unmanned station with a waiting room and without CCTV.
Southbound trains from Tyndrum leave around 15 minutes after they leave BoO, and northbound ones about 12 minutes before they leave
for BoO.
Again, if the waiting room was left unlocked all night he could have sheltered there overnight and taken the first train south in the morning. It's possible that the guard on the last train of the night locked the waiting room and the guard on the first train in the morning unlocked it, but given that this was a remote location it may have been left open all night. In any event I'd have thought a guard would remember a cyclist boarding the first train of the day (similarly at BoO).
It's also possible that Tony sheltered at one of these stations overnight and then continued his journey by bike the following morning, but if so surely he'd have had to stop somewhere not too far away for breakfast.