There is no set time limit to a throw-in, however, if the referee deems it being/taking to long he/she may warn and or give yellow card. Goalies have a soft time limit to punt or put ball back into play after they retrieve with hands. Ref may think they are wasting time and letting clock run by holding onto ball too long. Yellow card for that is more common. I have never seen a player get a yellow card for not throwing it in in a timely manner. It could happen similar to the goalie rule but not as common.