For me it depends on the customer. Some I would be quite happy to leave it for many months, and some I wouldn't.
For example, I clean a doctor's house whose also a friend of Wor Lass's from her running club. He'll wait till he's six months in arrears, then pay me for those six months and for the next six months ahead. Once those six months run out, he'll go into six months into arrears. We never arranged this, it's just the way it's evolved.
But another account I can think of, a young couple whom I suspect live above their means, I start getting twitchy at the 3 month point when they owe me for three cleans. But they always pay with an apology.
However, to be honest, 95% of my customers are long term good payers. I guess over the years I've dumped the ones who were reluctant to pay, or they've dumped me.