A.C.
My daughter was 10 weeks when I returned to work. Take it from me...your son is going to be much less traumatized by this than you are! I returned to work mid-week (half-days) and used the first few days to ease myself in...I wasn't "officially" back in the office until the following Monday. I was breastfeeding her and she had only had one bottle up to that point, so it made sense not to torture me, her, or her caregivers. I found that I was still very tired and it was a great treat to go home after half a day.
I also sent a blanket or toy that had slept with us so she would be comforted by a familiar scent.
When Monday came, I was full-speed ahead. I was close enough that I would occasionally go over on my lunch break, but at some point it was conflicting with nap time, and it was just a disruption to us both. I relished my pumping breaks because I really needed a time-out from the day.
Good luck. The daycare will be understanding if you call 10 times a day for the first few days...but, I'll be honest, what they tell you will never be the right answer. Either he'll be screaming his head off (and you'll cry because he's upset)...or he'll be just fine (and you'll cry because you think he doesn't need you).