I like this one:

Dekatrian Calendar (translated to english)

Calendário Dekatrian (original)

May be useful:

SI is great, but if you reset everything (and lose all tech and most of knowledge), just create a new system. Embrace what makes SI great (easy conversions and a the nature-based properties) and do it over.

For length, use Hydrogen line when you advance your society enough. It's more universal than using 🌎 as a 📏.

Will you use the sea borders instead of the coastline to avoid the paradox?

I didn't even know that neutrons have an antiparticle. TIL

Edit: neurons -> neutrons