No its not when you go to sleep its how much sleep you recieve. If shes getting her reccomended amount of sleep, including naps, for her age (12-15 hours) then its fine. Lots of people stay up, work, and even shop at night an it doesn't effect their brian. Everyone has different biological clocks and infants are commonly up later or earlier then we are used to because in the womb they have no set sleep times. The body needs time to recouperate and repair itself when you sleep but its the act of sleeping thats important, not exactly when.Lots of people let their children stay up late just as lot of people put them down early. It just depends on what works best for you. 2 am does seem a little late but not because it would cause any mental or health problems, but just because you may want to go to bed before then. If you'd like her to go to bed earlier try just putting her to bed 15 minutes earlier every other day (add 15 minutes to the last 15 minutes and stick to it, make sure you get her to bed and don't skip those 15 minutes.) And also adjust her naps by 15 minutes. Put her doewn for her naps 15 minutes earlier and wake her up from her naps 15 minutes earlier then when she would generally be up. You probably would also want to shift her feedings by 15 minutes as well so that her whole schedual adjusts.