We try to as a minimum go for a drink to sort out set lists and so on if someone is missing. We have had practice with just bass and two guitars, no singer or drums before and that was really productive. But generally we sort out the next few Thursdays in advance, everyone knows Thursday night is band night but if partners are working away or there's something of a one-off that has to happen on a Thursday night we try to give at least two weeks notice.
I like my band, we are all on the same level of commitment and respect for each other.