Sentence:  He also had , at times , an uncanny absent-minded air like a sleepwalker ; he would look right through you while you were talking to him , and if you said , `` For Christ's sake , Donald , you 've got Prussian blue all over your shirt '' , he would smile , and nod , and an <WSD>hour</WSD> later the paint would be all over his pants as well . 
Meaning of the word marked with <WSD> tags:  a period of time equal to 1/24th of a day