I do my Qbank questions in the morning, which seems to put me in the minority I guess. I prefer to do them in the morning. I figure that I will be taking the exam in the morning, so I better be ready to tackle questions first thing in the morning. I used the same approach with the mcat. It has worked just fine for me, although I have noticed on those mornings where you're dragging a little, that first block of questions can be a little rough until the caffeine kicks in.
I guess it depends on your study approach. I did a fairly extensive review of everything prior to my dedicated study time, so my main focus is on Qbanks. I'm doing ~3 blocks of 46 questions every day, which means a lot of time spent on questions obviously. Then I am re-reviewing everything in the evening with other sources like GT, Pathoma, FA, etc. It sounds to me like you might reviewing a subject, and then doing questions on them in the evening? If so, you could always just shift that over, so you study something in the afternoon and the next morning do questions on it.
I don't think it will hurt you to do questions in the morning though, and if you're more focused when you do them and review them, then it may help you more. Plus, if you're starting to get fatigued in the afternoons and that's when you're doing your reviewing, then you can just throw on a video review like Pathoma and do something a little more passive and just listen while your brain recovers somewhat.