Why are all the clock stuck at 4.20 on pulp fiction?

" There is a persistent myth that that all the clocks in the movie are set to 4:20 (although, certainly all the clocks on the wall in the pawn shop are set to 4:20). However, in at least two scenes it is obvious that this is not the case. In the "Bonnie Situation" while Jimmy, Vince and Jules are drinking coffee in the kitchen, the clock clearly reads 8:15. Secondly, when Vince and Jules go to retrieve the briefcase, it is "7:22 in the a.m.". The significance of the time 4:20 is that it is slang for smoking marijuana "