I'll go first. Across the five communities I advise right now, the median ranges from about 3 hours to almost a full day.
The fastest one doesn't have more staff. Moderators check a pinned new-members feed with their morning coffee, and that's it.
The slowest relies on notifications alone, so newcomers' posts get buried under replies to older threads.
If you track this, I'd love to compare notes. A rough range is plenty, no need for exact numbers.