I think the short answer is no.
I'd never say it's impossible for a larger multiplayer environment since I don't know the code nor am I a programmer. But it wouldn't be persistent either way in the truest sense the word. Sure you could save and load games but just ripping out new player characters and such wouldn't happen as the game stands.
The interface ain't made for it either which would be a massive problem even if you got beyond what the game is coded for playercount wise. There's no capacity to assign that many characters.
Turn timers are easy. They are built into the arena mode already, though I don't know how they work.
But you could script them either way:
//Start the process
IF
ObjectTurnStarted(_Player)
THEN
DB_TurnTimerChar(_Player);
TimerLaunch("TurnTimer",15000);
//Timer runs out
IF
TimerFinished("TurnTimer")
AND
DB_TurnTimerChar(_Player)
THEN
NOT DB_TurnTimerChar(_Player);
EndTurn(_Player);
//Ends turn normally
IF
ObjectTurnEnded(_Player)
AND
DB_TurnTimerChar(_Player)
THEN
NOT DB_TurnTimerChar(_Player);
TimerCancel("TurnTimer");