`self.last_check` is the last time this function was called, so moving it out to another function does not seem correct to me. This function could be named `file_modified_check` I suppose, but that seems redundant.  I think this change actually improves the situation because previously `last_check` was being used to compare against modified time. This could cause the problem you describe.

Now it is only being used as a reference to the last time this was called, so for your use-case (verifying modified time), this change actually resolves the issue I believe.