Hi L.. My baby is now 5 months old, but I can remember back (hopefully!) to 3 months ago. He nursed every 2-3 hours and since I've been back at work I try to pump every 3 hours. When I pump for 15 minutes I get 4-6 ounces so I assume that's about what he eats when he nurses - so when we bottle-feed him he gets 4-5 ounces. So I would say for a 3-month old, anywhere from 3-5 ounces a feeding is fine. Some babies like to "snack" and eat less at more frequent intervals. If it seems like this is what he's doing I would just have smaller bottle amounts to offer him. Try giving him 2 ounces and if he's hungry again in a couple hours just give him another 2. At that age it's best just to nurse/feed him when he wants it. He'll get into a more set schedule as he gets older so don't worry! He also is probably getting more from nursing and may prefer that to a bottle - so he may be "catching up" when he nurses
For bedtime, I feed my baby at about 7:30/8:00 and he's usually out after that. Sometimes he will wake up at 9 or 10 and want a "top-off" and then goes right back to sleep. Again, I just go by his queues.
hope that helps, good for you for breastfeeding and pumping at work! I know how much it sucks! ;-)