How would you choose a number, lets say between 1 and 500, and keep it for 24 hours, then automatically choose another one using PHP (and mysql possibly)?

I plan a "number of the day" feature...

You could build a script that creates the random number and store in a mySQL db as you mentioned (or even a flat text file).

The easiest way to do this on a 24/hr cycle is to setup a scheduled cron job that executes at midnight everyday. If you don't have cron access, you could have an extra field in your db or flat file that give a timestamp of last modified and check that data for each time the script is manually executed.

PHP Code:

if (is_file('randnum') && time() - filemtime('randnum') < 3600*24) {
   // read the number from file
}
else {
   $number = rand(1, 500);
   // write the number to the file
} 


Sounds like an exciting feature