Why not "temps" instead of l'heure? As in they give their time to work for a good cause
"Le temps" being also "the weather", "l'heure" avoids any ambiguity.
It depends on context. There is a good reference here: https://www.laits.utexas.edu/tex/gr/no5.html
Why not ils ?
Both Ils and Elles should be accepted.
I put that too. It makes no sense not to be accepted.