Bristol Gorilla behaviour.
I'm well aware Bristol will only take a short time, but with travelling times included I think it works out just fine (main motive for going is to spend a bit of time observing a functional gorilla group for the first time in 4 years - since Jersey, i've only been to Twycross and London which have gorillas)
You are exactly right over it fitting in with your travel time. Be aware the buses from Temple Meads station are frequent but take you on quite a roundabout route around some of the smarter suburbs before arriving at the zoo.(maybe 20 minutes plus-can be irritating when you are impatient to get to the zoo)
Re the gorillas- while they are a functional (breeding) group don't expect to see very much(if any) interaction. The two females Romina & Salome tend to stay well away from each other, so their respective offspring stay with their mothers. 'Romina' is often near the silverback 'Jock' much of the time and as he spends nearly all the time indoors, so does she (and her daughter). Salome & Komale(son) are often outside in the windbreak shelter- last time I went she was keeping as far away from Jock as possible to the extent of staying outside if he was inside, and vie versa.
Jock usually only comes outside for the 'feed & talk' - your best chance for photos. Both the females give him a wide berthwhile he is eating...

down near the moat and you can get good photos. Provided its not bad weather in which case they just do the talk inside.
Things may have changed somewhat though since the arrival of the younger handraised female 'Kera' who I'm told is in with the others much of the time now and I have not been since she arrived. Maybe she will create more play activity with the two youngsters, particularly the elder one, Namoki.
They are certainly worth seeing but don't expect a 'busy' active group such as at Howletts/Port Lympne as they are not like that- at least not yet(still not enough animals and also the two adult females aren't related so there is not a strong 'family' bond which is what really makes for a cohesive group.....)