2 hours? wow, that's good timing. Is that just straight extract, propane burner and wort chiller? I guess that's feasible if you have the right equipment, but that just sounds so short.
If these are your first two batches, I'd put aside extra time. If you had your system running for awhile and went through a batch like clockwork, then I'd say give yourself 5 or 6 hours for two batches. That's assuming you're using a chiller, using a propane or electric (220v) burner, got extra pots, and you're not sitting there reading and re-reading instructions. If it's your first time and you're using basic equipment, I'd worry about one batch for the day. If everything goes smoothly, go for the second. I'm kind of a newb, 15 or so batches, most AG or PM, and I've learned to leave extra time. Just because my last batch took 6 hours, I still leave myself 8. Something always seems to come up to make brew day longer. Then again, I have two young kids and a wife that's very unsupportive of my brewing, so It's not surprising to have her ask me to go out to the store and get her lettuce or tampons in the middle of a brew day. There really isn't an answer to your question. It could take two hours, or it could take 6. It's all dependent on your equipment and how well you know how to use it.