Your challenge, should you choose to accept it, is to either...
a. Prevent the French Republican Calendar from being abolished in 1805.
or...
b. Have the calendar be adopted at a later time (like how it was re-adopted by the Paris Commune), for a period of at least fifteen years, by an established country. Calendars based on the FRC are acceptable.
The parameters:
---The ten hour day must be adopted as well.
---You cannot change the original FRC in any way, though you can have limited reforms later on, or calendars based heavily on the FRC.
---The calendar must reach wide usage in the country where it's being adopted.