Hmm...
Another book I read (I posted the name in the book forum) said you actually need to make the bedtime earlier, as you thought. The reason they start waking earlier and earlier when you put them to bed later and later is because they are not as well rested at night, which messes up their day, then messes up their night again. Nasty cycle. This is fine for infants under 2 months, but as they get older they need an earlier bedtime. It messes with their biological clock if you put them to bed later. They author explains why, but I'm not sure I completely followed it.
If your lo is taking a late afternoon/early evening nap between 5 and whatever, eliminate it and move the bedtime back to whenever that nap begins. Chances are that's when bedtime is really supposed to start. Bedtime should wind up somewhere between 6 and 8 pm.
I didn't believe it until I bit the bullet and tried it (since nothing else was working). My lo went from sleeping 8-9 hours at night to sleeping 11-12, and I got her naps back (which were pretty much non-existant, and was the whole reason for moving it back...the extra 2 hours came with it). We were putting her to bed at 9:00...we moved her bedtime all the way back to between 6 and 6:30. Granted, she gets up between 6 and 6:30 every morning (sometimes she'll sleep till 7), but that works out well for us since we have to get up then anyway, and gives us the evening to ourselves. The average is 7 pm bedtime. They don't automatically start sleeping longer, they may still wake early, but then you feed them and throw them back in bed until a more reasonable time. Eventually they start sleeping longer as they become more rested.
Can't hurt to try it for a few nights to see if it helps.
*HUGS*
Sonya =P