It depends. In the hands of trained experts, with the proper protocol done beforehand, the answer is 2 minutes... but the fact that you're asking this question concerns me that:
1. Your thinking of doing it yourself at home - if this is the case, please reconsider. Glycolic peels of this strength can really cause serious damage if not done correctly, including permanent scarring.
2. You've perhaps had it done by someone, and feel like it may not have been done correctly, and you're checking with the experts after the fact to be sure. Be sure the person performing the peel is a board certified "core aesthetic" physician - meaning a dermatologist or plastic surgeon.
Don't gamble with your face.