I will add on to what Insidious said. But before I list the cons of this idea, I will explain why it is uneeded. If someone intends to come on our servers just to freekill, you can bet anything that a player complaint will be up in less than 30 seconds. People also just often call in an admin to take care of it, or the person freekilling just leaves immediatally after they freekill.
Cons:
If you join a server and see that you have to wait 10 hours to play CT you'd most likely just leave and go to a different server that doesnt have this.
If you had to have (Blank) amount of hours minimum to join CT, ratio would almost always be terrible due to the people who do have (blank) or more hours wanting to play T instead of CT. If we had the minimum amount of hours to join CT thing, we would either have to force the people with however many hours to join CT, thus them enjoying their time here less if they did want to join T; or our ratio just always being terrible.
The only reason this would be a good thing is to stop people who want to immediatally freekill, however they could always just wait out the time and still freekill. All we would be doing is wasting every 1/100 persons time who want to freekill; but also making our server a little or a lot less enjoyable for the 99/100 people who just want to be playing CT, or the regs who want to be playing T.