The movies change it based on what creates tension or is funny in the current situation.

In X-Men the Last Stand he is able to survive disintegration that goes through people around him in about a second by constantly healing the damage back (and his pants repair themselves too I guess). And a similar thing happens when he survives a nuclear bomb in the Wolverine. In Origins: Wolverine he is able to heal back from an adamantium bullet to the head fairly quickly but loses his memories.

Deadpool is supposed to have a stronger healing factor but it still takes something like hours to a day for his hand to finish growing back after it gets cut off in his movie.

I doubt the comics are much better about being consistent with the amount of retcons and changing writers that happen.