Well, if every change requires indexing, this must be a nightmare to administer. No wonder it can take weeks. I also didn't take into account that updates could introduce malware, but that's really a different issue.
Being hidden from search on a launch day will hurt visibility, even if you are doing advertising elsewhere. For instance, if you make a trailer for multiple platforms and a customer sees the itch.io logo among them at the end and decides to search, nothing will show up.
And yes, the page will be already available, but the fact is, you get cut from a very important functionality for an arbitrary amount of time even if you finish setting up your page months ahead.
Anyway, at this point this is just derailing into a rant, I'll stop :P
Thanks for clarifying the situation!