On the question of when to mill,it's best if you get right on it but I've cut oak that was on the ground for most likely over 20 years.Oh you get a lot of waste but you still can salvage some usable stuff.The drops,ends,etc you just toss in the wood stove,it all gets used one way or the other.
I pile the logs off the ground on top of cross pieces to prevent ground contact and seal the log ends with "Anchor seal".This stuff helps to prevent the logs from splitting.As they dry,the logs lose moisture faster through the ends that through the cross grains,thus the splits.Anchor seal or some other type sealants,paint too,helps but doesn't eliminate all this splitting.
As far as the chain getting dull fast,yes indeed it does.Although a lot of folks prefer a ripping chain,a standard chisel does a pretty good job and is a sight faster.
The picture is a pair of planks I carved out a while back.I think the log was about 16 or 18 inchs and I could make about a foot a minute.The planks are 8 feet long.