This sounds more like something that belongs on eeggs, the fact that it alternates between noon and 4:30 probably has some strange meaning. I, however, have no idea what it could be.
Personally I think it was just because they had to film the sequence quite a few times to get it right. The picture doesn't leave Walken's face for a while during one part, therefore it would have been pretty hard to get it right without being able to edit it.
there are a lot of rumors that all of the clocks in the movie are set to 4:20, which is a drug reference. The only clock in the movie that is set to 4:20 is when Butch is going back into the shop basement to help Wallace. Walken's watch, the Wolf's watch, even Brad's watch, and the clock in Jimmy's kitchen all display different times.
As the film is shown through peoples memories and points of view, maybe Butch didnt know the time as he was a kid when given the watch and now a grown man so he didnt know what time it was and thats why it changes