I almost always arrive late (flying from Denver, long flight, two hour time difference) and I have had pretty good luck lately but have to wonder if it has anything to do with my TA making the requests. Back when I booked on my own, I never got my requests. In any case, I have arrived as late as 1:00 a.m. at CSR, CBR and ASMU and gotten my requests met each time.
I would just be prepared for anything and remember that if you don't get it, to ask if you can be moved the next day if its that important. Sometimes not getting it is the best thing, I asked for Mansions at POR, got AB and loved that section!
I also agreee your request of a certain building(s) only are a lot easier to give on Disney's part than some of the "I need this building, this floor, on this side" etc type requests. I have travelled with family members before and seriously their lists of requests were about as long as my kids Christmas lists.