In addition to toolic's fine advice sometimes I like to fully qualify the calls; exporting nothing. Especially where the module is used in a single point in a longish bit of code. Saves a trip/grep around. So-

use Date::Calc ();
# 500 lines of unrelated fun.
my @what_what = Date::Calc::Today_and_Now();
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(update, added comment, fixed typo.)