Why do you add couscous to boiling water?
You don't really 'cook' cous-cous, it's already cooked - you just need to rehydrate it sufficiently, without getting it too wet &amp; going sloppy.

Starting with boiling water give you a better time-reference - 5/10/15 minutes from that known start-point, depending on the specific cous-cous type. You switch off the heat as soon as you add [or in many cases just pour water onto it fresh from the kettle then let stand.]

Starting from cold would introduce an unknown variable - how long does it take to boil?