You might check into how calm the daycare setting is. We had to temporarily use a place that blared loud adult dance music while some of the kids slept (not all of the babies slept at the same time). Our youngest son (then 6 months old) was completely fried when we picked him up. The lights were always on and there was no time EVER to calm down. Absolutely crazy! Look over the rooms carefully and make sure you understand what the daily schedule is like. Maybe he's not really getting a true nap (are the lights turned down? is it quiet?) or maybe they have him so hyper-stimulated when he is awake that his nerves are on end by the time he gets home. Do they engage in calm activities or is it always high energy fun? You might also check to see if they are feeding him anything you don't know about.
That said, with our older so, we had similar issues when he was a baby (at our normal daycare, which has a very calm program). At the time, my husband was a stay at home dad and we put our son in daycare for 2-4 hours a day so that my husband could have a break. We found that about 4 hours was the tolerance limit for him as a baby (once he was past 2, it didn't seem to bother him if he stayed longer). He would be really crabby if he stayed longer. This held true even after my husband went back to work.
In any case, I would predict that this is going to change as he gets just a few months older! Good luck!