i don't specify a time for domestics as if i don't get paid that month i know i'll get double the following but never let it go more than that.
14 days for both residential and commercial.if payment not made in 14 days(BACS/SAE customers)i send a text reminder.for some commercial they pay a bit later(usually within 28 days) but i always get paid in the end.
Payment is due on completion of job. That said, I don't chase customers for the money. I collect when I am local to them, and sometimes leave it till next time if they are ones I know I can trust. John