I often do reduced agitation development on sheet film in trays for night log exposure photos or other high contrast shots. I have had no problems agitating every five minutes, though I usually do three minute intervals. I have not tried going any longer yet. One precaution I take is to cover the entire tray with a larger tray during the "stand" periods.
When I develop this way, I experiment the first time by figuring out a time based on the total percentage of total development time in which there is active agitation. For instance, if I normally develop HP5 using dilution H, my time for normal contrast is 15 minutes, I normally agitate about 15 seconds out of every minute, then I know that I agitate for 3:45 minutes total, plus one minute at the start, for a total of 4:45 total agitation. If I use double dilution H for stand development, I double this. So I want 9:30 of total agitation time. I give two minutes of constant agitation to start, just to get the film somewhat evenly developed and burn out some of the developer activity right off the bat. Then I agitate for 30 seconds every three minutes until I have reached 9:30 total agitation time. 2 minutes initial, then 30 sec. out of each 3:30 fifteen times. Because of this timing, every cycle, I end up "flipping" to the opposite thirty seconds of the minute.
As you can see, this takes an hour per shot. To save time, I do several sheets at once, all in different small trays. I put 4x5 film in 5x7 trays and 5x7 film in 8x10 trays, and cover all the little trays with a big tray. I have done 4 4x5 sheets at once and two 5x7s at once, but no more.
Sounds convoluted, but it has worked surprisingly well for first guesses, with little adjustment needed.
I generally like the results of stand development best on large format. The reduced solvent activity really lets the grain go to town, but it shows up as a unique form of "micro sharpness" (to make up a term on the spot), but without actually showing the grain like with smaller formats.
The rubber band method in a hand tank sounds interesting. I would like to try it. My only fear would be that the bromide streaks might become too directional. I would probably want to change the orientation of the tank after each agitation, like I do with roll film. When I stand develop roll film, I do it in an open tank designed for developing sheet film. After each agitation, I turn the reels a different way. Sometimes on their top, sometimes on their bottom, and sometimes on their sides.
