My experience suggests that the mailing out of subscriber mail is done in batches every few minutes, perhaps a little longer at busy times.
I note that when I edit a post it normally gets a note attached giving a date/time when it has been updated. However, often when editing a post very soon after posting, it does not get that note. I assume that the note is an indication that mail has already been processed for that message and subscribers will have received a different version that that now seen on the forum.
Volunteer Helper - but recommending that users move off the platform!
Once the admin for GregHelp now deleted.