Random amount of milliseconds wait()?

Hi there,
so this is a simple randomizer I made,

-- ============================================ --

--             start rngWait function           --

-- ============================================ --

function rngWait(value)

   rng = math.random(value, value*2)

   return wait(rng)

end
But I need something to work in milliseconds.
If anybody can throw a bone, I'll be happy to throw you a coffee back.

Cheers!