Lat and or rowing moves already hit the biceps quite well. Probably why they are getting exhausted and will only respond after so much inroad. In fact I only do heavy rowing and back work almost exclusively with a set or so of curls a week at most and my biceps are as big or bigger than when I did direct bicep work 3x per week.
2.5 hours is a long W/O for the whole body, let alone just the back and arms. I'm going to guess you are putting perhaps too much emphasis on the smaller groups, that will only respond if the entire body is getting larger and stronger with mass on the big areas and groups. Also, if you are cutting cals, you will most likely be trimming size some.
That all said, if one has to wait 2-3 mins between sets for some recovery, then fine. Sometimes I might wait up to 4 or so mins. between heavy deads or squats.