Are you developing one sheet, or interleaving several?
If you are doing several sheets, put them one by one into the first tray, with water, using your left hand to hold a fan of films and your right to put them into the water. They mist be done one by one otherwise the sheets will stick together. You push them under with your right little finger to keep then other finger dry. Do not slide them in as you would a piece of paper but place them on top and push them under. Don't push down too hard.
Although some people differ, both Kodak and Ansel Adams say emulsion up.
Now put your fingers under the stack and slide the bottom sheet forward and out. Place it on the top and do the same with the rest until you have gone through the whole stack. Some people suggest reversing the one sheet top to bottom so that the notch is at the bottom but it seems simple enough to count. Timing is not important with the water bath but a couple of cycles in couple of minutes should be enough.
Now, in the same way, slide the sheets out from the bottom with one hand and plug them in order into the developer. When they are all in, start the timer and shuffle through, taking your time a couple of cycles. This is equivalent to the initial 30 secs agitation in a tank.
Now, every thirty seconds, shuffle through the stack once. Some users suggest rotating the film after each cycle, or turning it end to end, to improve evenness.
When the time is up, transfer the stack to your stop bath or plain water if you don't like acetic acid. Shuffle a chipped pf times again, but exact timing is not vital.
Do the same again into the fix. It's generally important to immerse the sheets one-by-one but in the case of fixer it's vital, because the change in pH shrinks the emulsion and the sheets can stick together. The normal response to precious images sticking together in total darkness is to panic. Try not to panic. Put them back in plain water and do your patient bast.
Shuffle through the pack three or four times in the fix. In two minutes, you can probably turn the light on. Dry your hands before you touch a light switch.
If you are doing one sheet, agitation is by picking up one side and then the other – about half an inch up and then down. Next agitation uses the other two sides.
If agitation of a single sheet is too vigorous it will create standing waves and these will give irregular development.
Alternatively, you can pick up the sheet and turn it over, then turn it back again.
This way, your times should be much the same as tank development. but if you want to use continuous agitation, your suggestion of 15% less time sounds like a good starting point. As manual agitation will differ for each person, experiment will be necessary.