Hi,
You wont be able to swap colleges I'm afraid as it's university policy unless you have an incredibly good reason (usually only on the basis of health/ religion etc.) I guess if your food allergies were especially severe and a doctor recommended self catered you *might* be considered, however they are also quite likely to point out that in catered they will be able to cater for you, and that in self catered sharing a kitchen with other people actually makes it more likely that cross contamination etc. will occur (no matter how careful you try to be). However I wouldn't be too worried, the catering in my experience is very good! Time wise, every meal time takes places over quite a long time so you have some flexibility in when you eat.
Breakfasts have some hot options (including egg, beans and veggie sausages) and also toast, cereal, fruit, yoghurt etc. I think it's served between 7.30 and 9.30 ish?
At the weekend Brunch then includes all the above plus pastries, and normal lunch stuff like salad and sandwiches. I believe this is from about 11.30am to 2pm? If you want to be up early they also do breakfast at normal time too.
Lunches normally include 4 different hot options, 2 vegetarian, and you help yourself to carbohydrates and vegetables. There is also a really nice salad bar, plus pre made sandwiches (lots of options) or a 'deli' option where you can make your own having chosen your bread and filling. For lunchtimes when you wont be in college you can also order a packed lunch which includes what you would expect! This is from 11.30 to 2pm
Dinners again have 4 hot options, 2 of which are always vegetarian, plus the same self service of carbs/ veg/ salad. There's also pudding. You can also get sandwiches if you prefer cold food in the evening. I think dinner is usually 5-7.30 ish? You can also order late dinner too if you're going to be out!
They're also incredibly good at catering for food allergies! I have friends who are lactose intolerant, coeliac or have nut allergies and they were all ok!