Thumbs up for your call on the final once-over. Don’t rush that revision—you’ve got several months before any of those requestors even bats an eye. They’d all tell you, very sincerely, to take as much time as you need to get the manuscript right. That said, if I were you I’d aim to finish the revision and submit no later than six months after the requests. It’s not that they’ll hold a time lag against you (they know that post-conference revising takes time and that sometimes Life gets in the way), but rather that the marketplace could shift in that time, as could the very jobs of those agents and editors. I certainly wouldn’t wait longer than a year, which editors commonly use as their limit when they extend open submission invitations at conferences.