Roughly whatever it says on the can/box If she drains it everytime, increase it. I did this but whilst DD made it look easy, DS was a pickle who chewed bottles dribbled a lot and waited till next breastfeed! I gave up doing bedtime bottle in the end (back to breast) and did bottle at approx 3pm instead which he at least attempted to drink!
Does it work? (as in, how much longer will LO sleep for?) Sleep deprivation is really starting to get to me so I'd consider it. Can you do it for one or two nights a week or would LO expect it every night?