Then is time you take the oath is not idiomatic English, but the English of a non-native speaker: the character who speaks this line in Rise of the Guardians is represented with a Russian (or Russian-ish) accent. Consequently, the question of how the verb should be parsed is irrelevant.
In context, after asking "Are you ready now, Jack? To make it official?", what the character presumably intends is
Then it is time for you to take the oath.
... meaning that since he is ready, the appropriate time has now arrived.
It is possible he means:
Then it is time you took the oath.
In this idiom, the past-tense took would have a modal sense: you should take the oath, you have postponed or evaded that obligation. This meaning seems to me very unlikely in context.