A collective noun denotes a group of individuals regarded as a unit. Collective nouns may take either singular or plural verbs, depending on whether the word refers to the group as a unit or to its members as individuals. In American English, most nouns naming a group regarded as a unit are treated as singular (see 7.5.5, Collective Nouns).
Fifty percent of my time is spent on administration.
Fifty percent of all physicians are included.
At noon today the jury delivers its verdict.
The team practices every Thursday.
The committee decides who will receive tenure.
For a unit of measure, use a singular verb (see 17.0, Units of Measure).
Five milliliters was injected.
Two weeks of symptoms is common and should not be cause for alarm.
Fifty million dollars was awarded to the discoverers of the vaccine.