Yeah, setting basic nap times is a great idea for biorhythmical reasons. As soon as your lo wakes in the am, his biorhythm is pretty much set for the day.
The first thing I would start doing is getting him up at the same time every morning, maybe within 15 mins or so. The more consistant each day is, the more he'll come to expect to go to sleep at certain times, and his little body will be ready for it. A good time would be the average time he wakes every morning.
Now what I do is keep my lo in her crib the whole nap, unless she cries out to me. If she's fussing or playing, I just leave her in there. I get her up no sooner than after 1.5 hours, and no later than 2 hours, keeping an eye on if she wakes or sleeps after 40 mins. The longer you let your lo sleep in the am, the harder it's going to be to get a good afternoon nap, so if you can, I'd limit the am nap to no more than 1.5 hours net. What I believe I'm teaching is that she needs to be sleeping during this time. Most of the time if she wakes after 40 mins she goes back to sleep (sometimes with my help) after 10-30 mins or so. She usually wakes and plays after 40 mins, but I know she's still tired from experience. If she really is rested, she lets me know. If it's a short nap, I try to push her wake time as close as I can to the next nap time, keeping things really low key, but not so much that she gets waay overtired.
As for naps times estimate them based on how long your lo can stay awake, and that will be your base time for the nap to start. You put them down within a half hour of that time depending on how long the first nap was. If the first nap is skipped completely, put him down within an hour of the afternoon time. The cat nap runs the same way if you still have it.
This doesn't guarentee that your lo will sleep as long as you need him to, but it keeps things a little more routine for you. There will be days where things will get hairy, but that's normal. As your lo can stay up longer, be sure to push the nap times up too. If the afternoon nap time is skipped, be sure to make bedtime earlier by about an hour, but not before 5:30 or so. But bedtime should be around the same time every night.
The important thing is to keep wake time in the am and bedtime as consistant as possible, because that sets the biorhythm for the day.
Hope this helps!
*HUGS*
Sonya =P