The rule of thumb with all sorts of ''rolling" processing is to take the recommended time minus ten percent. If you use a diffusor enlarger - you'll need a bit more contrast in your negs then - I always take the recommended time. It takes a bit of testing out.
Some diffusors are softer than others.
Sticking the various comparative times in a spread sheet shows that Agfa reduce the time by an average of 15% for Rotary processors and round up or down to the nearest minute
This gives times for Rodinal of:
Kodak Tri-X 1 + 25 6 min ISO 500/28°
1 + 50 12 min ISO 500/28°
Hope that helps, I do have a full Agfa data sheet somewhere for Rodinal which I know does have the times for a wide variety of films and includes Rotary processors. The times I've given are only rounded up by 3 & 6 secomds !