These two expressions are used in both hyphenated and non-hyphenated form. Which do you use when?
In situ is a Latin expression meaning “in the place.” When used as an adverb, there is no hyphen; when used as an adjective, there is a hyphen.
The microbes for the project will be cultivated in situ. (adverb telling where cultivated)
The field will be developed using in-situ combustion. (adjective modifying combustion)
Similarly, real-time is hyphenated when used as an adjective, and not hyphenated when used as an adverbial phrase with the preposition “in.”
Fiber optic cable enables temperature measurement in real time. (adverbial phrase telling when measured)
Real-time data are essential for directional drilling success. (adjective modifying data)
How shall we remember this?
If there is a noun right after it, hyphenate it. If not, don’t.