The oldest radioactive dating is uranium lead quantities and zircon. Oceanic fossils and minerals give us a estimate of height of primitive oceans. And the oxide mineral contents of geologic strata give us estimate of how much carbon and oxygen were in our primitive atmosphere.
Take a look at the work of John Valley at the University of Wisconsin. He has dated zircons from the Jack Hills in Australia. Now, he is analyzing glassy inclusions in zircons. The inclusions are unaltered siliceous magma that formed the crust of the early earth. The American Geophysical Union published a volume of papers you should see. The book "...
For dating old geological material, zircon dating is sometimes used. Also see Uranium-lead dating. There is also data from Antarctic and Greenland ice cores.
Other things you could look are Earth formation theories - the core accretion model & the disk instability model as well as plate tectonics and continental drift.
There are also the theories about ...
Models are set up with a calendar (length of year), and run using that calendar - there is, usually, no interpolation to any other calendar afterwards.
Yes, seasonal cycles in the forcing are adjusted to the relevant calendar - say 360 days.