The importance of an early bedtime.

An early bedtime is extremely important for infants if you want to achieve sleeping through the night. The natural time for a baby to have bedtime falls between 6-8pm.

The following is a great explanation from a resident expert from BabyCenter:

It is, if one wants the child to consistently STTN.

STing [sleep training] on teaches the child how to put herself to sleep. Just because a child knows how to sleep does not automatically mean that she will STTN. To achieve the state of "consistently STTN", the child's sleep needs must be met and be in sync with her natural sleep rhythm.

Some believe that as long as the child is still somehow clocking up 11-12hrs of nightsleep etc, e.g. 9pm - 9am; it will work. But it does not. What actually happens is that in that 9-9 time frame, the child will have multiple nightwakings and willrarely sleep longer than 3-4hr stretches at a time. If one is STing, this means unnecessary crying every 3-4hrs; which not only fragment nights but means that the child is overtired as some hours of sleep is lost every night due to crying and nightwakings.

ETA - note that almost all parents with poor sleepers insist that their LOs are "natural" late-risers. When kids are up a few times every night, they do appear to "sleep in" because they are SO overtired and trying to catch up on sleep. However they very rarely STTN, even for a minimum of 6/7hrs for 1 year old; while those that BOTH know how to sleep and is on an appropriate sleep schedule is consistently sleeping 11.5-12hrs straight every night by 8-12 months.

A child's natural wakeup time is only apparent when she is well-rested and consistently STTN. The wakeup time that one sees when the child is up several times all night is artificial and certainly *not* natural.

Is early bedtime a must?

We have found that a bedtime of 715-730 works best for Boston. Establishing a bedtime routine helps greatly in getting babies to sleep. They learn that these things happen in a certain order and that means it is time to sleep. An example of our bedtime routine can be found below. You can do anything you want in your bedtime routine, just try to keep it the same every night!

1. 645pm Bath time
2. 7pm Dry off, get in pajamas
3. 715pm Last feeding before bed
4. 730pm Put in swaddle/sleepsuit
5. Read part of a book
6. Lay in crib with Baby Einstein soother on and turtle (makes stars on ceiling) with lights off

I've mentioned this link before, but My Baby Sleep Guide is a great resource for anything to do with night sleep & naps. Most of your questions can be found and answered there. The following post from this blog has average times of night time sleep for the different months:
Night Time Sleep - What's Average
And this one has a lot of great suggestions on figuring out what you'd like to do for your pre-sleep routine:
Pre-Sleep Routine