Often from the movie we hear that the actors and actresses suddenly use the past tense in thier speechs. I just don't know what is the grammar rule behind that. Following are the exapmles:

a) Actor: Look, it's time we forgot :-s about the rule.
b) Actress: Honey, I think it's timeI met :-s all your friend.
c) Actress: I think it's time we told :-s them the truth.

Could you tell me why they suddenly use the past tense?
This has nothing to do with acting or actors.
The expression "it's time" is normally followed by a clause in the past tense. It can also be followed by a clause in the present tense, but the past tense is more common. Whichever tense is used, the meaning is the same.

This turn of phrase is a substitute for the "for ... to ..." structure.

"It's time we forgot about the rule" = "It's time we forget about the rule." = "It's time for us to forget about the rule."
"I think it's time I told them the truth" = "... time I tell them the truth." = "... time for me to tell them the truth."

The implication with these is that, whatever it is, it probably should have been done sooner.

Emotion: geeked
Students: We have free audio pronunciation exercises.
Thansk for your reply CalifJim. I got it.Emotion: big smile
What is the past form for heroine?
banana desk 923 What is the past form for heroine?

Heroine is a noun. It doesn't have a past tense. Only verbs have a past tense.

Students: Are you brave enough to let our tutors analyse your pronunciation?