I dumped most of mine I weaned in Oct in Jan and did fair.
As far as weaning strategy goes is about money I don't have a month target I have a dollar target. I have sold at four months and I have some I am stll holding from Oct. You have to be flexible.
You have to watch the market like a hawk and pencil out when you think it's best to sell. I have a minimum I target for on the calf crop and sell when the calfs will pay that. I always figured it is better to have a bird in the hand than one in the bush, overall that has worked for me. This year's target will be 570 a calf which is 78 dollars over last years operating cost, this is a 6wt calf at current prices. You can't run at max and do this you have to have enough pasture or hay to hold your calf crop, this another reason I adocate there is no such thing as to much hay. When my operating cost was 365 per cow my minimum was 440 per calf.
There are different strategies depending on weather, food availabilty etc.
Around here, commercial STEERS and heifers bring the most when they are black, weaned, vaccinated and around 600-650 lbs. That is if you are taking them to the sale barn.
Otherwise, if you can work a deal with a feedlot (but it takes connections) you can get premium price for your weaned, vaccinated calves.
The calf buyers in Alberta seem to want at least 650 lbs...preferably weaned. In fact there are fewer and fewer people wanting calves at all? The feedlots prefer yearlings and pay a premium for steers over 900 lbs.
To get a 650 lb. calf by fall you need to calve fairly early and fewer farmers are willing to do that anymore? Why knock yourself out when you aren't going to make any money anyway?
The late calving crowd either carries the calves over or soon goes broke. A 400 lb. calf at 95 cents doesn't pay for the cows upkeep. You can only lose money for so long before the wolf is at the door!
The higher the price of corn is the more the buyers want you to put the weight on and not them. If the price of corn drops to below $3 we might be back to selling 500 lb calves. I would agree that now you are better off selling 600-700 lbs. I have tracked the market here in North Carolina for several years. As a rule of thumb you get 50 cents for each lb you add to the calf above 500 lbs. You have to decide how much that lb cost you to see if it makes economic sense.
Edit: edit to add that prices are usually a little better in the spring than in the fall after mid September.
So if you are adding the weight above 500 between August and November you may not make anything, again in a normal year. We have not had many normal years lately.