1) an unspecified period of time, generally used when you wish to impress upon someone that you've been waiting for them much longer than desired.
2) the nebulous "suggested" amount of time recommended before venturing into a place where you have done something immoral, illegal or where something unpleasant has happened.
1) "Shit man I'm sorry, how long have you been here?"
"A good minute"
Many people think a good minute is as good as a minute, but in fact it is much better. If I tell you that I ain't had no Church's in a good minute, you better believe it's been a couple of months AT LEAST
Bizzlitz Masta: man I ain't had no Church's in a good minute.
Desmond: yea I know man. We ain't got no Church's since the first National Treasure flick hit the newsgroups.