Same here—in fact, I just put a second deep on one hive this past Saturday. The other one has had its deep on for about two weeks. The third hive is a split, so it probably won’t see its second deep for another couple of weeks.
The NUC bees are still a ways out before they’ll be productive. Overwintered bees are in swarm mode, so make sure you check them weekly through June. If you have overwintered bees, I’d consider adding a super just to give them more space, (even though they really need the space in the brood box) but a super can help.—but place a queen excluder below the supers. Once the super starts to fill with nectar—and I mean across all the frames—remove the QE. It slows the workers down, since they have to squeeze through.
The main nectar flow here on the Palouse usually starts around the last week of June, but it can begin sooner. I like to put on a super a bit early—sometimes as early as June 1st—especially in a hot, dry spring (which we haven’t had this year).
On another note, be sure to check your bees for mites. This is the time of year when mite numbers can begin ramping up fast, and you don’t want to hit the nectar flow with high pressure. There are treatments that can be used during the flow, but always read the label—some have temperature limits.