This is because of people like (You know who) and (You know who this is as well) who basically create variants in five minutes, get 10 testing games in 10 minutes, and submit. If you really believe in your variant, you won't really have a problem with this rule. For example, take The Ripple Effect, made by me. I was slightly annoyed by the 24 hour rule over there, and it got hopelessly autodeclined.
Why does VW have a 24 hour rule for testing gameplay?
It is to make sure you do not rush your variants.
Also, even if you’re really confident in a variant being really good (which is and maybe should be most variants imo), the time gap between the first game and last game can help clear your mindset so you can spot things if you overlooked any issues earlier
Variants World is a system for submitting chess variants. Many popular ones are on Chess.com because of that website. I create variants sometimes, and I want to know - what is the purpose of the 24 hour rule for testing games? If you are the CGA reading this, then please tell me.