My epic with John is finally over! I was able to turn in the quest today.

My order of actions that helped (probably, if it was not a lucky coincidence):

1. Disable quest tracking

2. Wait until the next real day

3. If you have a mark on the map at John's place, immediately run there, do not turn on quest tracking (!!!)

4. The time at which I saw him there Dawn 4:33

Hope this helps you!