It's a good question, but it's necessary to understand that a bank garnishment is not a single event, it is a legal process that unfolds in time, and that the procedure is different from state to state. In Kentucky, for example, the bank has 20 days after receiving the garnishment writ to respond. But, the debtor also has at least that same amount of time to object to the garnishment or to claim that the money in the account is exempt from garnishment (ex. Social Security payments). Right there three weeks are down the tubes, at least. Then it's back on the judge's desk for a final order. Courts are fairly efficient, but there is no telling how much time will be involved. After that, it goes back to the bank which will be given a certain amount of time to pay the money to the creditor. It could be 10 days, in Kentucky, but it might be more and it might be less. Nothing iron-clad.
So, we a talking more than a month from beginning to end, easily. But it could be more.