my golden rules:
- 1+100 (5+500 / 10+1000)
- 20C or 24C doesn't seem to make much difference
- make sure there's at least 5ml of dev per 135 or 120 or 4x5, mostly that limits to 1-2 rolls or sheets per tank.
- Invert 3-4 times only at the start, and never again (if you invert a second time after 5 mins, or after 45 mins it doesn't matter much when, but you'll risk blowing highlights depending on how high you exposed)
- After 1 hour the dev is mostly exhausted anyway, 2 hours or overnight won't do much extra (I only do longer if the tank is full).
- Experiment.
In short, the whole point of a stand is to locally-exhaust the developer around the highlights, then give it extra time working on the shadows. Semi-stand will mix it all up and start again so you get double the working on the highlights and they could blow out. If you don't touch ityou can theoretically leave it for days and you'll get the same result (but I haven't tried).
Also, having the dev closer to room temperature is best by my theorising. If the dev is a lot hotter or colder than ambient, eddy currents will start to happen. If the dev is the same as the air, it'll stay perfectly still which is what you want.