hi, assuming you are going to be at the lawns...
Theres a bus every 10-20 mins or so. one bus comes every 20 mins, that goes to hull via uni, n there is another that comes inbetween n goes straight to uni.
both busses take between 15 - 20 mins to get there, so usually when you have a lecture, it starts at 15 past the hour, so you get the bus from the lawns about quater to the hour, get there for around the hour or so, depending on traffic etc. that give you just enough time to walk to lectures and get in n sat down etc, or nip to the loo or shop etc, depending on where you are on campus etc...
bus pas it like £160 for the year, but you get unlimited use on the busses (apart from the late bus at like 2am, but no one uses that neway....its cheaper easier n quicker to get a taxi) so can go to town, or uni an unlimited amount of time, even just using it to nip into the village on the booze run, its proves invaluable..!!!
dont worry about it taking longer to get to uni or out, i have friends at other unis who have to set off before me on there walk to uni....
hope this helps.
Rob