Some devs interrupt what they are doing when they see a PR in a Slack notification, most don't.

Most devs set aside some time at most twice a day for PRs. That's 5 hours at least.

Some PRs come in at the end of the day and will only get looked at the next day. That's more than 5 hours.

IME it's rare to see a PR get reviewed in under 5 hours.

I use a PR notifier chrome extension, so I have a badge on the toolbar whenever a PR is waiting on me. I get to them in typically <2 minutes during work hours because I tab over to chrome whenever AI is thinking. Sometimes I even get to browse HN if not enough PRs are coming and not too many parallel work sessions.

But there's more than one person that can review a PR.

If you work in a team of 5 people, and each one only reviews things twice a day, that's still less than 5 hours any way you slice it.