How did 7 years pass?

Question

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?

Answer 1

Reff: Predestination Explained
There is a handy time-line diagram if you need in that link

The instructions that are left by Barkeep is for John to follow is given to John 7 years after he's made to join at the HQ. Assuming John starts training to be a Temporal Agent in the year 1985, 7 years later, he goes on his first mission. 1985 + 7 = 1992. His first mission is given to him in the year 1992, 7 years after he has last seen Barkeep.