The best antibodies in the colostrum are in the first 12-24 hours. Freezing colostrum at 24 hours will be fine. Not only are the antibodies important, but the thickness and richness is also necessary for the gut tract to help the calf pass the meconium. So many think that the first 12 hours are the ONLY colostrum...but there are reasons why most cows have the thicker richer milk for 1-3 days. Old rule of thumb was to hold a cows milk out of the tank for 6-8 milkings even if no antibiotics... now some farmers will put it in after 2 milkings if it "looks white". Try to educate them with results of the milk sample test we do on dairy cows...
If you freeze it, and then you have a calf born on a sat night, and nothing open or convenient, don't you think that it is better to give 24 hr colostrum than plain old milk replacer?
A hint: DO NOT THAW IN THE MICROWAVE. It destroys all the healthy stuff. It is irradiating the food, basically making it sterile. I freeze mine in 1 qt and 1/2 gallon containers. The qts are easier to thaw in hot water. They say to get 1/2 to 1 full gal in them within a few hours of birth. I try to feed colostrum for at least 2 feedings. I will feed colostrum to anything I buy unless I know where it comes from and the farmer does a good job of starting it. A 2-3 day old calf might not be able to absorb all the antibodies, but I have found that they just seem to do better if they get that in their system when I get them.