Hyphenate adjectives, not nouns

"Object-oriented" is hyphenated, but "use case" is not.

• run time – noun, the time at which the system runs (not hyphenated)
• run-time – an adjective describing something which exists at run time (hyphenated)
• runtime – noun, the run-time support, e.g. the VM (portmanteau word combining "run" and "time")

”Run-time errors are caught by the runtime at run time.”

See also: Hyphens Between Words