['The time of day in which craving, withdrawal, and other tobacco abstinence symptoms are assessed may moderate the influences of abstinence or medication on those symptoms.', 'Participants were 209 smokers participating in a 4-week crossover study assessing symptoms due to smoking versus abstinence and while using nicotine (21 mg) versus placebo patch when abstinent. None was trying to quit permanently during the study. Abstinence was verified daily by a carbon monoxide level of less than 5 ppm. Participants completed craving (two measures), total withdrawal, and positive affect (PA) and negative affect forms three times per day: in the morning, upon arrival at the clinic in the afternoon, and in the evening. All comparisons of the effects of time of day, abstinence, and nicotine patch treatment were within subjects.', 'Results showed a main effect of time of day on all measures while smoking, wherein PA was higher and the other four measures lower, during afternoon versus morning or evening ratings. Time of day interacted with abstinence on both craving measures, but not the other measures, such that abstinence increased craving less in the morning versus the other times. Time of day also interacted with nicotine (vs. placebo) patch effects in alleviating negative mood to a greater degree during evening versus morning or afternoon ratings.'] Does severity of tobacco abstinence symptoms vary by time of day?