You can fly as much as you like with an FAA certificate, provided you are flying an N-registered aircraft
But not for compensation or hire (commercial ops), with a few excemptions
If you`re asking about a validation, then I think the period of validation is (still) 1 year. The main idea behind this (I`m guessing) is so that you can keep your flying skills up to speed while converting to JAA/EU/EASA ATPL
If I were you I would contact the Swedish JAA for the correct info, as there may be some local, national variations. Happy landings!