Why are we discussing anticipated arrival delays,forecast bad wx, local knowledge of extended routing etc in a thread about "contingency" fuel?
Those things are what "extra " fuel is for.
You can burn all your contingency at the holding point prior to departure.(assuming you never anticipated that hold and loaded "extra" gas to cover it)
If you are anticipating it it aint "contingency".That's for unforeseen things like non forecast headwinds or routings.