But if the index doesn't update you won't notice.

Yeah, search isn’t an OLTP system.

I pretty strongly doubt that the arrival rate of new docs at search is an order of magnitude greater than that at Gmail.

Offtopic, but it blows my mind seeing <1 min old StackOverflow comments indexed by Google search, the sheer amount of work going on behind the scenes to make that happen.

I'm pretty sure this only happens when the site is actively pushing updates to google via their webmaster tools. I think your sites importance would also impact how fast google indexes it.

Didn't realize this was a thing: https://developers.google.com/search/docs/guides/submit-URLs

Although I'm not sure if this is what stack exchange actually uses or if there's some private API for big partners.