Quoting Cuterest:" Grocery stores in my experience usually take 3-5 business days to clear a check. The reason why checks ... [snip!] ... go through so fast sometimes is when the person you wrote a check to banks at the same bank as you. (I use to work at a bank.) "
Or many companies have a machine that deposits the checks whenever someone decides to do it. (We have one in our office. It remotely connects to our
bank, and we have to tell everyone don't hand us a check unless the funds have already cleared the account.) Sometimes it takes a few hours, but most of them, even checks from other banks, clear pretty quickly.