Please define 24 hours.

I can do 25 moves on my phone, and do 25 TT problems every 24 hours.

Please explain to me exactly when does this reset? Does it reset back to 0?

If I normally start my TT positions at 6pm weekdays, can I do them at noon on weekends?

I'm asking because lately I've been getting messages saying I'm on my limit, and I dont remember having an issue a few weeks ago.

http://en.wikipedia.org/wiki/Day

so, considering if chess.com used GMT, you should look for the GMT equivalent of your region. this how i figure when tournaments start in my region. if it didnt work, mark the 25 moves you made in specefic time like 09:00 P.M. then wait for more than 24 hours, then see if your 25 moves are reseted or not.

if either did not work, see what is the offical system reset. i mean when every thing in the site changes, puzzles, articles, etc.

i believe it's a rolling 24 hours. so look back 24 hours, and if you've done 25, then that's it. as time passes, those fall off the rolling 24 hours. 

Thanx :)