When they get a bank levy, it's only good for money in the account at the time it was executed. They take whatever funds are in the account, up to the amount of the order. After that, the order becomes discharged.
That doesn't mean they can't ever take from your bank account again-- it just means they have to keep going back to court and get separate attachment orders each time they want to levy your account.
Keep in mind, every time they go back to court for a new withholding order, probably $85-150 is being tacked on to your balance in court costs alone. If you have a means to make payment arrangements without them having to garnish, you will save yourself some court costs.