Albert Barnes Commentary 1 Samuel 13:8

"And he tarried seven days, according to the set time that Samuel [had appointed]: but Samuel came not to Gilgal; and the people were scattered from him." — 1 Samuel 13:8 (ASV)

Had appointed — This appointment, of course, has nothing to do with the one made years before (1 Samuel 10:8), which is explicitly mentioned as having been kept at the proper time (1 Samuel 11:15). On this later occasion, however, Samuel had again set an appointment for the end of seven days. This appears to have been a test of faith and obedience, a test which, this time, Saul unfortunately failed.