Not been to a graduation at Strathclyde, but I sometimes work for Ede and Ravenscroft (the company that supplies the gowns), so have seen a lot of graduations from the 'other' side.
The student should get info from the University telling them when to arrive/pick up tickets and gown. With larger ceremonies (some have 500+ students), there may be staggered times to arrive.
Strathclyde's website says "You must be on campus at least 1.5-2 hours before the start of your ceremony to make sure you have enough time to collect your tickets, gown and to register. You'll also need to be seated in the hall 30 minutes before the start of the ceremony."
That is a normal sort of time, IME. If you're having official photos done, it's best to get them done before the ceremony, so you're not hanging around after. The queues for photography can be LONG.
I'd recommend arriving 2 hours ahead, and getting the gown collected and photos done, then you can wander around, even go for a late lunch if there's somewhere close by. If the student doesn't want to wear the gown while wandering around, there will be gowning staff on site to check they've put it back on correctly before the ceremony.