The short answer is: until the judgment is paid in full. In the mean time, the collection attorney is adding fees and there is interest accruing. You would almost always be better served by making voluntary arrangements with the creditor's attorney than letting the debt be satisified by garnishment. The only time that might not work is if the creditors are lined up to garnish your wages, then paying one will just make room for another to garnish.
If it is a consumer debt, I'd recommend you consult a lawyer familiar with the FDCPA to see if the collector has done everything by the book. NACA, the National Association of consumer's attorneys has a nationwide referral service.
If it is not a consumer debt, and it is quite large, you might come out ahead by hiring an attorney to negotiate a settlement or payment plan. It could save you more than it costs.
In Virginia, garnishments last for 90 or 180 days with exceptions for taxes and child support. The creditor has to file a garnishment summons. The summons will have a court date. That is the date that the garnishment stops. However, the creditor can file another one and start the process over again until the judgment, interest and costs associated with collecting it are collected.