Function to determine if a file is newer/older than timespec

I would like to be able to define a class if a file is newer or older than some time specification.

For example, if a file is older than "3 days from now", or "January 21st 2019".

Currently we have functions that can compare files to other files. While it's possible to calculate the times I might want, and create files with those ctimes, its quite fiddly.
See changedbefore, isnewerthan, isolderthan().