[Drakker]

Depends on the hop-up system really. A well installed r-hop should stay the same. For hop-up rubbers it depends on the type and brand. I find that harder rubbers have a longer break-in period, but that's my impressions and not science. I find that most of the time softer rubbers are good to go right out of the box.

My non-scientific hypothesis is that regular rubbers need some time to "sit in" properly. Once you are done installing them there is some "stress" left in them, especially when using a one piece hop-up chamber where you have to painstakingly push the rubbers in. They move around from shots and vibrations until they sit in a position where they stop moving. I find that AEG rubbers in one piece chambers take a lot longer to break in, versus VSR rubbers in two piece chambers, but that might just be the reason why VSR rubbers are considered superior to AEG rubbers anyway.