The following check for gtimeout means that other OSs that don't have the expected behaviour in either command won't break the script, you'll just get a warning message that isn't terribly relevant to them (but more helpful than simply failing or silently running without timeout/gtimeout. Perhaps improving that message would be the better option.

Though for that snippet I would argue for testing for the command rather than the OS (unless Macs or some other common arrangement has something incompatible in the standard path with the same command name?).