The short answer is 'whatever you want an episode to be' - though Cyndi brings up good points about superlong episodes which i agree with.
A Legend (of some sort) was designed where each page has a gag/joke/event that makes it semi-self-contained, even if there is an ongoing story arc, similar to comics like The Order of the Stick, Dumbing of Age, Menage a 3, etc. So I post one page at a time - with the vertical scroll format, they can seem like some pages are longer than others, but they all end up on Standard Comic Pages when read in the (hopefully eventual) print format.
Do whatever feels right to you!