I believe they will have to do that soon with calves sent over as time is running out to make the sacrifice unless they have others in the queue. With that said I would like to see this unfold.
As far as I know, the calves have to be at least in their third year (2 years + one day or more), but I don't think there is an age restriction beyond that. Of course, the older they get the more likely something might happen to disqualify them.
Before Oct.7, there had been talk about doing the sacrifice around Passover, but that was just because they wanted to, not for any specific religious requirement.