In Arhu's canon, "active power" means hyperstrings, the lines of power that make up the universe's energy, powers spells, enables worldgating, etc. If that doesn't exist in this version of the universe, or it would take a different form, I'm totally cool with that ^^ It's not like he'll have any idea what it is, anyway.

Canon has given no specific limitations to time spent sidled as far as I can tell, though there's a warning that spending too much time in alternate planes leads to forgetting one's self, which is implied takes several weeks. As an initial echo, I'm perfectly happy limiting the time to, say, an hour? Half an hour? Whatever you feel is reasonable!