Ooh, I can’t wait to see your version of TagTime!
@narthur: Official Reference Implementation of the TagTime Universal Ping Schedule
(Googling “tagtime reference implementation” turns that up and you can also find that and other handy links at tagtime.com (let me know when I can add your version to that list, @smitop!)
@smitop: As for the question about a stateless function to get the next and last ping without walking forward from the beginning of time, I don’t think so. Now I’m curious what language/framework you’re implementing this in!