In 2004 or 5, Congress and the Federal Reserve created a new program called "Check 21" which allows merchants to submit checks electronically, which means instantaneous debit. Not all merchants or commercial financial institutions offer this, but you probably wouldn't know if the place you're writing a check does or not. It's best to write a check only when you have the money in your account. Basically, you can no longer count on the "float" time.
By the way, Check 21 also changes the way you can get copies of the check. Because the recipient may send an electronic copy of your check to your bank instead of the actual check, then you may never see that check again, nor will your bank. If you needed it for any records or a copy, you would only get an official electronic check (which has any and all capabilities of the original paper check).
My career experience at the credit union