That is hard to answer without knowing what you are making this from.
As a rule the warmer the fermentation temperature the faster it goes.
If you are in the mid 70's to 80's F that would not concern me.

Joe

Ceri Jones wrote:
> I put my yeast (ADY) into the primary about 5 hours ago, 2 hours after that
> there was a layer about 1cm thick on top, now it's bubbling!
>
> I thought it would be slower than this - is it normal for yeast to be this
> energtic? They've had no extra nutrients other than the must itself and my
> Very hard water.