the longer you let it run the better...one or two days may get you some filter bacteria, but not a lot. in fact I run an extra filter on my tank of platys and guppys all the time, that way whenever I want to start a tank I have a precycled filter to start off with.
the extra filter creates more flow then a male betta might like, but it works well for livebearers.
the extra filter creates more flow then a male betta might like, but it works well for livebearers.