Consistent long term use is your best bet. I do three sessions of 2:30 each every day in the shower. I take the occasional break (usually on days that I am shaving done there). I have been at it for a few months now and have seen some minor permanent gains (1/10”).
If you are looking for a quick temporary gain I suggest taking a bath and doing 5 sessions of 3 minutes each, resting for a minute or two between. This gives me an extra 1/2” or a little more of girth temporarily. I suggest putting on a cock ring immediately after drying off, and using the erection pretty quickly - the temporary gains seem to go away within an hour or so for me.