How recent is "recent" in the following message?
You have already edited 5 of your own posts today (not including very recent posts). Further edits are not allowed until tomorrow. Please contact a moderator if you require assistance.
According to this post by @Marc Gravell♦, it appears that "(today/yesterday)" is considered recent. That question also includes information about why the rate limit is in place.
Based on how the term today is used elsewhere on the site, I'd assume that it means posts created on the current UTC day and the UTC day previous to that.