Heh, sounds like something we're going through.
I've been doing the same thing. If mine wakes before 6 am I just leave her in the crib...she's usually cooing/fussing anyway, but 9/10 times she just goes back to sleep. But ours has also been doing the 45 min nap thing lately. And yeah, when she gets up that early and doesn't fall back to sleep, she's usually back in bed for her first nap between 7 and 7:30.
Our solution is to put her to bed even earlier for awhile, and see how that works. We put her to bed between 6 and 7 before...the other night we put her to bed at 5:45, and she slept straight through until 7 am...and we had to WAKE her up at 7 am in order to get a good ~9 am nap in. In total, she slept 18 (!!) hours yesterday, something she hasn't done for a few months. Last night wasn't so successful, as she woke up at 7 after we put her to bed the same time and didn't fall back to sleep until 8 (a habit we've been working on getting her to break, as she's been doing this every other night or so, however, she was overtired when she went to bed). However, she still got up at 6 am, no earlier. BUT, she's on her second nap of more than an hour right now. So, our solution is working so far. We may move her back up to her 6/7 pm bedtime in a week or so, we're just trying to get her more rested at night again (12 or more hours).
Biologically speaking, if you don't get a good solid afternoon nap in, or your lo is not taking a catnap or solid nap somewhere between 3 and 5 (when they're supposed to be getting 3 naps a day), then it's a really good idea to get them to bed for the night earlier than usual so they're not drastically overtired by bedtime and won't/can't sleep well...but usually no earlier than 5:30 or so to get them rested well that night, although I've heard of other babies going to bed at 5 pm. If your lo is between 9 and 12 months, you still want to get them to bed late afternoon/early evening until they are old enough to start playing with their sleep schedules a little bit, as they can handle it.
This is generally speaking of course. Most follow the early to bed, later to rise rule though, but there are certainly exceptions!
Hope this helps a little! Don't be afraid to experiment with his bedtime a little bit, especially if you're going to put him to bed earlier. That may solve your problem. The more rested they are, the better/longer they sleep.
*HUGS*
Sonya =P