One of my 737 manuals says for the Classic it's 5 mins for T/O, and for the NG it says 5 mins or 10 mins OEI.
My other company's 737 says 5 mins, but for a few hulls it's 10 mins (no mention of OEI).
That leads me to believe that, on the 737 at least, that there are options.
I'm guessing that this is really for the bean counters, and not for the pilots. Who wouldn't set radar power if we're going down, Larry?