Stepper the 205 day weaning is a benchmark. Mostly for grazing herds, born in April weaned in Nov. Normal conditions is to use the grass, that by Nov is getting lower quality. Good to get the calves off the cows when the feed is getting short and poorer quality.
In dryer conditions calves should be weaned earlier, ideal conditions it's OK to leave the calves on another month or so.
Its cheaper if grass is in short supply to put the feed directly into the calf, rather than put it through the cow to produce milk.
I don't think calves should be weaned under about 450 pounds, to much stress on them, and their digestive systems aren't ready for a all roughage diet, and it takes some time to get them on grain.
I think calves that are over say about 550 pounds adjust well to feeding good hay and grain.