Seems to me those few seconds (of exposure) are negligible when you consider the time spent handling the paper and running it through the various baths. There must be some more practical reason -- does it make dodging/burning easier to have the safelight off during exposure time? I don't do enough of it, so I don't know.
That's why my safelight (just the one over the enlarger - I have four in my darkroom) is connected to the timer. It's easier to see what you're doing when you dodge and burn. I occasionally check my lighting to be sure it's safe, and even with several minutes exposure, there seems to be no effect on the paper. I do pre-expose it a little before the test. I use old red safelights with 15W bulbs.
Moma don't take my Kodachrome away!
Oops, Kodak, of all people, did!