Sealing up valve covers

I have both stamped steel and aluminum covers on my two 440s and I have found that the gaskets will relax and become slightly loose after sitting couple of hours (around a 1/2 to 3/4 turn) and I will retorque several more times over several days (at least once a day) till the torque stabilizes at the factory torque setting. Have had no leaks doing it that way.