Why even do it all then?Make it one challenge per season. If you waste it in week 5 don’t come crying later when a playoff berth is on the line.
I have never understood why challenges are limited beyond the need to have a time out available. You are penalized a missed challenge by losing your time out. I don't understand why you can't challenge as long as you have a time out remaining. So you can challenge 10 times in the first half and get them all correct (the whole point of making replay challenges available at all is to get a call correct) as long as you have a time out to lose if you get it wrong. I also think you should be able to dip into your second half time outs (in the first half) if you so desire.