var number;

function wait_seconds()
{
    wait(-3);
    number = 1;
}

function mything()
{
    number = 0;
    wait_seconds();
    while(number != 1)
    {
        //do stuff
        wait(1);
    }
}

function fnc3secs ()
{
   var clock = total_ticks + 48; // 3 sec * 16 ticks/sec
   while ( clock > total_ticks )
   {
      wait(1);
   }
}

var timer=0; 
while(timer<3) //3 seconds
{
   timer+=time_step/16;
   wait(1);
}