Recipe timer protocol idea

Have had this half-baked idea for an open source recipe timer protocol.

Eh?

Let me explain. People would tag up recipes with start times and
durations of each step of preparation in a standard way.

Then anyone could create apps to read those recipes and present them
in a useful way.

Eg, imagine a timer app that read a "roast lunch" recipe. It might use
the tagged timing data to give you cues in real time what to do:

Boil the kettle
Pre-heat oven
Put fat in tray
Take the sprouts out
Add the stock

The benefit is that it would be much easier than following a recipe
that requires you to calculate all the timings backwards from ready -
such an app would effectively be telling you what to do when.

But I imagine other people would create other more useful apps if
recipes were tagged up in a standard way.