When I sell at a show or in my studio and take a credit card, the money takes 3 - 4 days to hit my bank.. When I take a paypal sale, the money take 3 - 4 days to hit my bank.
I sell on one site that collects the money for the sale (amazon) and I get a settlement every two weeks and that takes 3 - 5 days to hit my account.
I sometimes need access to the money quicker for postage, but mostly try to keep enough in my stamps.com account to cover what I may need..
there are times during the year when it is a bit tougher ( for me, it is March-April, part of May-June) and I try to prepare for that.. but then life, weather, politics or natural disasters happen.. always something. (this year it was a tornado hitting my daughter's house, and my husband having to get flown to a medical center for an emergency pacemaker)..
the upside is that when sales patterns get established, the settlements are like little pay checks - and help me manage my money a little better.
but that is just me.