A calfs digestive system cannot absorbe the anitbodies after 24 hours of age. But, if you have some extra , I've never seen the harm in feeding it for seve4ral days. This is just a personal thing, but I thing the added nutrition of the stuff sure can't hurt and maybe even helps give them a little boost. My old mentor used to feed it for 3 days, had very few sick calves and they seemed to alwasy do well. I wouldn't go buy the stuff, but if it's available, why not feed it?
I wouldn't buy much ahead of time. It's not hard to come by, but you could keep a bag on hand just in case your luck is like mine and you need some on a saturday night and the feed store doesn't open until monday.
I try to keep a pack of colostrum mix on hand especially when we have heifers expecting their first calf, If we're there we like to give them some right away , sometimes the heifer doesn't get the calf drinking as soon as she should . the colostrum mix also gives you some extra e-coli protection as well