Terms of Quantity
A. Most plural subjects require plural verbs, but nouns referring to measurements of money, time, or distance are treated as singular units.
Five hours is plenty of time.
Two dollars is hardly going to cover the cab fare.
Tightly packed in the duffle bag was five million dollars.
Six yards of material seems sufficient to finish the quilt.
B. If describing something singular in sense, other terms of quantity can be treated as singular units.
Three cups of sugar is what the recipe requires.
Is four revolutions in the air even possible for skaters?