Forum:Golem Sentry

the card golem sentry reads, "Once per turn, you can flip this card into face-down Defense Position. When this card is Flip Summoned, return 1 monster on your opponent's side of the field to the owner's hand." Because it says once per turn, am I able to flip golem sentry during any time other then my main phases? Also looking at lost guardian, moai interceptor cannons, and medusa worm, all of their effects include "during your mainphase".