I understand it now, that's a good idea, all at particular time ...
Did some testing and observing of behavior with the code I have using Crontrol plugin:
- If I have no scheduled ping search engine, and I update or add a post, the ping is scheduled for 24 hours.
- Any next change or update will generate a new sitemap after 5 minutes.
- Any next change or addition does not add any new ping schedule (no several events, just one). Also, if the schedule is 23 hours remaining, for example, it will not go back to 24 hours, but remain on track.
You can try it, I think even with your code, there will only be one ping event, not several.