I know utilities exist on Windows for this, but can't find anything on the Mac.

(Windows has: http://www.nirsoft.net/utils/run_as_date.html]

A utility to run an application as different date (than the current date) before/during its run?

We have a lovely animated advent calendar my daughter adores, but it's from last year, and all the days are visible from Dec 1st onwards, unless I roll the system clock back a year, which I sometimes then forget to put back after she plays with i, resulting in chaos!

Thanks