Well, I assume you'd have to log into that alt, it would grab all your "svings" and reset times, and when you log into another alt, the "reset date/time" would just be current date-time plus reset timer. I can look into trying to make it as well. Doesn't seem too difficult, never made an addon before though.
I'm going to work on this after work today
Just found this:
http://www.wowwiki.com/API_GetSavedInstanceInfo