I’ve realized that I can do something for an extended time and not quit but it just might take me forever. But when it comes to timed things I almost break. Any inputs?

The biggest thing to remember is that you are not working under the circumstances that you will when you get to selection. You don't have the pressure when you are out at the gym by yourself. If you are finishing the workouts then you are way ahead of your peers, I guarantee it. This is where I cannot completely replicate the feeling of being at selection for you. Keep it up and finish the workouts and you will be just fine. If you can find a workout partner, healthy competition will keep you on your toes as well.