WordNet 3.0 cited in the Free Dictionary:
Noun 1. time off - a time period when you are not required to work; "he requested time off to attend his grandmother's funeral"
You would say:
"I plan to take two hours' time off."
Wikipedia notes time off and Paid time off (PTO) in AmE:
In the USA, Paid time off (PTO) is a feature in some employee agreements that provides a "resource" of hours that an employee can draw from to take time off from work, without having to specify a reason.
Note that the phrase is also used in a broader sense or in various contextual meanings, such as time when you are not at work or at school (Macmillan), a period when one is absent from work for a holiday, through sickness, etc (Collins), A break from one's employment or school, as in I need some time off from teaching to work on my dissertation , or He took time off to make some phone calls (dictionary.reference.com), and such other.