I've shot some sheet of 5x4 FP4 film and developed them in Rodinal (1+50) for 15 minutes at 20C. The guidlines I;ve seen talk about agitation every minute or so, I've used a Jobo drum on a rotator that constantly reverses the movement every minute or so. Does anyone have any guidelines about this? Should I develop for less time as the agitation regime is more often. Maybe I should try some test sheets to determine the standard development times with my set up.

As you can tell, I'm new to this area.
Thanks in advance.