So what you'll do is you'll have to make use of a server time variable "timevar"/"timevar2" store that in a client string and then when the player comes to vote again, compare the distance between the current time and the recorded time, if it's greater than 24 hours let them vote again.
PHP Code:
function onPlayervotes(){
if (timevar2 - clientr.voteTime >= 24*360){
server.votes ++;
clientr.voteTime = timevar2;
return true;
}
else return false;
}
Of course to set a clientr variable you must be on the serverside and there you wouldn't have the player scope so you still have some work to do.
Good luck.