Hi Michelle,
How long has he been waking at those times? I suspect that it's not necessarily habitual, but related to his milestones. Often when a lo learns a new skill they want to practice, and nighttime is no exception. Since he's just learned to crawl and you find him on all fours it sounds like that's what he's doing. Assuming that's what's going on here, you want to keep these wakings from becoming habitual. I would suggest trying wake to sleep closer to the actual time that he wakes, like 10 or 15 min before rather than an hour. Or if you prefer, it will often take more than 4 days to see improvement with PU/PD.