I don't wait for the nosewheel to be on the ground before bringing in reverse. On landing, autospoilers are out, autobrakes are engaged, and I bring the reverse up while slowly lowering the nosewheel to the tarmac.
There are few airplanes I've flown in which I wait for the nosewheel to land before applying reverse thrust. Only on a slick surface is it advisable to wait, and to cautiously apply the reverse.
Of course, you need to know the airplane, and yourself; I brought the reverse in, just into Beta, in a King Air 90 once and it turned out to be badly rigged; I nearly went for a ride. It was okay once all three were on the ground, but not until.