Hi L.,
I haven't had a chance to read any of the other responses yet,so if your question was already answered, I'm sorry for the repeat! Anyway...
Formula, once mixed, can be left unrefrigerated for up to 2 hours. However, once that bottle touches your baby's lips, the formula is only good for 1 hour...it has to do with bacteria. I give my daughter room temperature bottles. I set up a few bottles of water (room temperature), and if she starts waking up and I think she is going to eat soon, I add formula to one of the bottles. I'm glad the bottle is good for 2 hours after that, because sometimes I'm wrong and she goes right back to sleep!
If you warm your bottle (and your little one ends up going back to sleep or whatever), you are not supposed to re-refrigerate OR re-warm the bottle later on. Once in a while I will read online that this is okay to do once, but according to my doc, that is not a good idea. Anyway, why chance it? I'd rather lose a little bit of money than to have my baby get sick!
Sorry, I don't know much about the drop ins with the rip-off tabs. I used to work at a daycare center years ago and we used those, but I really can't remember anything about them! Congratulations on becoming a mother...You are going to love it!!