If I could change one thing I did during my son's infancy, it would have been to not focus as much on scheduling his feeding and sleeping. I was pretty desperate for some semblance of order amid the colic chaos, and had a really hard time interpreting his cries as many moms can, since he cried all the time despite our best efforts. So, I was often unsure if he was crying for food, or for comfort, or for tiredness, and tried to figure it out by figuring out what his schedule may be.
The biggest secret I've learned with raising my son, now almost 4, is that he is not easy to predict, and can not be fitted to a clock schedule. His needs for more or less sleep, more or less food, and even more or less pottying vary from day to day, even now. I wish now that I'd just tried to feed him whenever he cried and ignored all the advice I read in magazines about not being a human pacifier, or about needing to get him on a schedule.
Since that time, I've asked a lot of mothers about this, and the ones who seemed to have had the best experiences, are the ones who didn't stick to clock schedules and responded, instead, to the baby's cues, even if they seemed to be at irregular times. I'm seeing this work out beautifully with my new niece right now. I can really see that she seems very secure that her caregivers will show up and fulfill her needs, whenever they arise. According to academic child psych, this is her primary task the first 6 mos, to develop that security in her environment and with her caregivers.
I remember how desperate I was that first year, and especially the first 6mos for some predictability and scheduling. Despite what all the parenting books, like "The Baby Whisperer," and magazines said, in my life, I think it made things harder for us, honestly, and may even have set us up for some of my son's current control issues. It's a big thing to say, but that really was my main regret.
If she's sleeping between a 10pm feeding to a 6am feeding, that's extraordinary among what I usually hear at 4mos. At about 4 months, my son slept for 6 hour periods overnight and it was a real blessing. He also seemed to start his night sleeping period around 10pm, though his range could be between 9pm-midnight. Sometimes, he would cut it short and wake up in about 4 hours for a wee hours feeding, if he was extra hungry that day. During the day, 4hours between feeding times was the max we could go with our son... but he was a breastfeeder, and the time period between feedings can be somewhat shorter than for formula-fed babies. 2-3 hours was more usual for us for at least 6mos. I tried setting a 3.5-4 hour schedule and it was a disaster.
All told, though, like other moms here have mentioned, I'd just go with what seems to make her happy. Each baby is different... and in my experience... each day's schedule can vary, too, even for the same child. If she seems tired earlier, put her to bed, if not, don't, especially if the timing works out well for you for a 6am feeding. Putting her to bed earlier could shift that wake-up time earlier, since 8hours overnight seems to be on the longer end of the normal timespan at that age.
Best wishes,
B.
p.s.
I just noticed several writers mention that 8 hours was either normal or not enough for a 4 mos old. This is the first time I've heard this; I normally heard that 6hour stretches were a good "normal" to hope for at 4mos. Eventually, they do stretch to more of an 11hr range, but at 4mos, that seems awfully long to me. It certainly didnt' work out that way for my son. So, I googled to find out what "normal ranges" may be published out there and found a great website with links so several sleep studies for infancy to determine what is ideal:
http://www.kellymom.com/parenting/sleep/sleepstudies.html
The mom who collected the links prefaces them with this:
"Probably one of the main reasons that babies who don't sleep through the night are such a big issue is that parents don't have realistic expectations of the sleep patterns of babies. Babies were designed to wake up often at night to feed and cuddle, and keep in mind that many adults wake during the night, too. If our expectations for babies were not so different from our babies' expectations for themselves, much of this "problem" might disappear."
It's food for thought.