Help With Health Regeneration

so this is my script to regenerate health but what i want it to do is wait 20 seconds then start regenerating. However if i just put another yield in there it waits 20.1 seconds the regenerates 2 health. So how would i make it start regeneration after 20 seconds

function Regeneration () 
{
    while (health < 100)
    {
        yield WaitForSeconds (0.1);
        health += 2;
    }
}

function Regeneration ()
{
yield WaitForSeconds(20.0f);
while (health < 100)
{
yield WaitForSeconds (0.1);
health += 2;
}
}

Should work. I don’t recall how Coroutines are done in js, but make sure you run it as a coroutine or your yields won’t work right.