You've gone from a 'basic' question to an FEA package. Blimey, there's a jump.
The principle is basically the same though, you need the forces involved. The timing isn't that crude, it's simply the time from initial contact to the aircraft no longer having vertical motion (that set of wheels is firmly on the ground).
Ground effect isn't actually a major issue as you know your sink rate (ground effect will alter that value, but if you have the value it isn't an issue). The bigger problems are things like sudden gusts or turbulence which could cause a heavy / not so straight landing. Increasing the load on the gear.