When the barkeeper takes John to the HQ of the temporal agents we see that the date is 12 August 1985 late night (11 pm if I am not mistaken).
Later, almost at the end of the movie, after the barkeeper goes back to 1975 to be decommissioned, we see John in his room with a recorder listening to some advices that the barkeeper is giving him, in particular, the record says something like:
When you'll listen to this 7 years have passed, the first mission is as important as the last one...
So 7 years, but the camera shows that actually the time is 13 Aug 1985, so it is the next day: what does it mean? is the timeline changing?