Have use clotrimazole for tinea pedis for a week, haven't seen change. now i see blisters. how long does it need to take action?

Lots more time: It can take a month before you see positive results and 3-6 months for a cure. The only thing concerning to me is the blistering you are experiencing. This causes me concern that you may be having a reaction to something present within the cream or ointment that you are using. If the blistering worsens and/or itch worsens a lot, consider seeing dermatologist to check them out.