When do all the sleep cycles reset?

Like when is the barrier between a nap(descending directly into REM) and going to bed at night?

I don't know of an exact timeframe for it - I think it's pretty variable, but generally, if you take a nap an hour or 2 after waking you should have no problem. 3 or 4 hours is much more iffy, and might already be too late? I would think 5 or 6 hours is way too late. Maybe you should experiment and keep journals so you can work it out, and then you could tell us!

It SEEMS like I've read somewhere that 6 or 7 hours is supposed to be the top limit, but I'm not sure, and I would definitely try to err on the side of less time than more.

Of course it will be different at times depending on your state of health and how well you're sleeping etc. - there are days when I feel sleepy all day and I think I could probably drop straight into REM at any point (I kinda feel that way today in fact, I ought to give it a shot). And if you're suffering from sleep deprivation, you'll be able to hit REM immediately at any time. Though it's not recommended to deliberately deprive yourself of sleep - very bad for your overall health!

EDIT:

Tied it. Couldn't fall asleep. It takes me at least like an hour, which is why naps don't really work for me. Oh well, it was relaxing anyway.

I believe 7 hours is about the limit. After that, any nap will consist more of nREM (slow wave) sleep than REM sleep, meaning there's very little chance of having a good dream, let alone a lucid one.

I don't think I can link to it here, but if you Google "best time to take a nap", one of the results has a "nap wheel", where you specify your wake up time, and it will show you the best time to take a nap for energy - where the amount of REM and nREM sleep is balanced. Obviously though, for more dreams you'll want more REM, so any time before this "ultimate nap time" is best for lucid naps.

I think that "it depends" is really the only reasonable answer, and I know that's not much help. I was a bit sleep deprived recently and took an afternoon nap that began about 7 hours after waking up, that lasted somewhere around 3 hours, and I recalled a great number of dreams upon waking up. Normally I don't remember much of anything from naps, but my naps don't usually last more than 45 mins-1.5 hours and are usually also around 6-7 hours after bed.