It is a misleading statement. The parentheses are only for grouping. localtime[5] will convert [5] into an array of date and time elements. This is not what you want because [5] is not a reasonable thing to convert to a time.

The parentheses are only to get localtime to be called without an argument.

Enclosing parentheses don't change context. Look up the dual-nature comma operator to understand lists and their parentheses. That the standard (i.e. Camel) example of a list includes parentheses doesn't aid proper understanding of this issue. But it is impressive how the dwimery works in spite of this.

Be well,
rir