After a kohen washes for bircat ha-kohanim, sometimes he might touch soembody else’s hand or somebody shakes his hand by mistake. What should he do? There is not enough time to wash again. What if a kohen is praying longer and finishes right before retzei. Can he rely on his morning washing? Should he not duchan?
Netilas Yadayim for Birkas Kohanim has the status of regular Netilas Yadayim. Therefore, if a Kohen touched somebody else’s hand while his hand was still wet, he must wash again. If there is not enough time to wash again, he may duchan without washing again, because bedieved, we rely on the morning netilas yadayim. The same applies for a Kohen who finds himself with insufficient time to wash: he may rely on the morning netillah, though lechatchilah, if he knows that timing will be tought, he ought to wash before beginning Shemoneh Esrei.
Sources: Rambam and Tosfos dispute whether there is an obligation of washing for somebody who washed his hands in the morning, and many poskim (including Mishnah Berurah 128:20, and including Peri Chadah, Olas Tamid, Peri Megadim, Chayei Adam, Magen Giborim, Kaf Hachaim, and others) write that one may rely on the Rambam under extenuating circumstances, or that even Tosafos agrees that one may duchan, bedieved, without washing, relying on the morning netillah.