Hi L.,
Each baby is different, as is each mother. My children could nurse and be satiated (full) in less than 5 minutes. While I have had friends whose children needed to nurse for at least 30 minutes in a feeding.
If you are at work for 6 hours. You probably need to figure that your child would nurse probably once or twice in that time period. Just make sure that you make up the feeding and feed them once or twice more when you are home. I do not think it is an issue, unless your child begins lose weight and your Dr. will be sure to keep you on track for that. At abourt 6 months, my son started to lose weight and I needed to take him back to the ped. office the next week for a weight check. He made the weight check, but only by one ounce. I tell you what, I was stressing out cuz the Dr. said I was going to HAVE TO supplement with formula! But since I nursed him as frequently as possible that week, we made the weight gain. The other reason I would not be worried either was because you only work three days a week, so your production should not really be affected. The way I see it, is your baby is only missing three feedings. Something that can easily be made up over the course of a week!
I also think it is a great idea to have daycare put breastmilk in the cereal or other food they are feeding him. I would not go to any great expense to try and find a new type of bottle or nipple. Just try and go with the sippy type of cup. The other thing you can remember is that many babies at his age sleep for longer periods than 6 hours in the night and they don't have any issues with their weight gain.
Best of luck with working and nursing. I loved nursing and found it to be a special time to spend with my babies!
Hang in there and good luck.