OK, now, I know I am a new user, but, judging by the amount of CB rares I have obtained in such a short time, I think I am qualified to give some advice.
Step 1: Learn the descriptions
Reaction times and internet speeds aren't the only things that matter. If you learn the rare descriptions by heart, you won't take as long to identify the rare and click. That gives you a huge advantage over people who have to read the description in full.
Step 2: Ethernet cables
This isn't a problem unless you have slow internet. I don't use Ethernet cables, and I can obtain CB rares. However, if you have bad internet, hard wire your PC to your router with an Ethernet cable. It will greatly increase loading speeds and make it that much easier to get a rare. Ethernet cables are availible online and Radio Shack or Home Depot probably has them.
Step 3: Accept your doing it wrong
The F5 method can work, but I have a much better one. Get all thoughts of F5 out of your head.
Step 4: Learn the better way
OK, by far the best way to catch CB rares is to do this. Hover over the biome in which the desired CB rare can be caught, or the biome with the least amount of people if you're not going for anything specific. Now, look at you clock. The second the time changes to a multiple of 5, drag your mouse over the egg on the far right. Then, quickly glance at the description. If it's a rare, click, and receive! You won't be the fastest every time, but this method in my experience works more than 50% of the time.
Step 5: Identify which eggs may be taken
This is the last step. If you don't get a rare, or even if you do, click around the biomes, and look for any rare or BSA eggs. Try to snatch the rares, and if not, keep refreshing the biome that has a BSA egg in it (if any do). That BSA egg will be taken soon, and a rare might drop. I have gotten 10% of my rares either 10 seconds or a minute after the drop by doing this.
Step 6: Enjoy!
You now have defeated the ultimate challenge, catching CB rares on DC with consistency. Tell your friends, your family, and the president.