TAG counting number of days since given date


I am trying to set up a command allowing to automaticaly return a number of days since a specific date (working like the !fc days count).

My aim there would be to get that kind of result:
Streamer did X mistakes during the last Y days

I will be using $(cmd_count) for the X value (no reset needed, so no need for $custom_data )

I would want Y to countup a number of days since a provided day (I thought about an inpout using the $time(DD-MM-YYYY) ).

Thank you for your help