Logic diktates that you have more time on the C210 because the wheels go up and down.
So why not allow your log book to reflect the conversion to the 206 in perhaps 2 hours followed at once by a conversion to the 210 in another 2 hours, followed by several hours flying in the 210 with an ending one hour in the 206? The nearest any one in Africa will possibly ever come to checking what you do is to see if there is a 206 or a 210 registered on the airfield where you are.