They certainly don't complain. Generally they are eager to perform, yes, and perhaps over time become bored. Standbys have to be within a certain distance of the theater, however I haven't heard before of an standby being REQUIRED to be at the theater throughout the entire show. It's probably true for Riley Costello because he is underage...
"The Spectacle has, indeed, an emotional attraction of its own, but, of all the parts, it is the least artistic, and connected least with the art of poetry. For the power of Tragedy, we may be sure, is felt even apart from representation and actors. Besides, the production of spectacular effects depends more on the art of the stage machinist than on that of the poet."
--Aristotle