He did not say that he had to drag the brakes for 5 to 10 minutes. He raised an issue when "on a descent for long enough – five, ten minutes, with constant braking."

Chris Froome says he's 'not 100 per cent sold on disc brakes' as he reviews his new bike - Cycling Weekly

I understand that to mean a descent with "constant breaking" over a 5 to 10 minute period.

With rim brakes one quick look plus one squeeze of the brake lever confirm I am good to go. I can do both as I am lifting my bike off the wall onto the ground. I don't have a bike with disc brakes but I don't think it is quite that easy to verify their condition. That said, by the time the brake tracks on my wheels are worn out, lightweight alloy wheels for rim brakes may no longer still be offered, so I will have to switch to disc brakes then.