To slay him in the morning - When they might be able to distinguish between him and Michal his wife; for, had they attempted his life in the night season, there would have been some danger to Michal's life. Besides, Saul wished to represent him as a traitor; and consequently an attack upon him was justifiable at any time, even in the fullest daylight.
Saul‘s plan was to surround the house at night, and to have David killed as soon as he came abroad unsuspectingly in the morning.