I really meant at first. I assumed you were just starting out. You don't have to be really sore. I think my point is... do as many miles as you can. Listen to your body.
You burn fat at a pretty constant rate, I think. And as anyone that has ever tried to ride in Ketosis will tell you... that isn't enough energy for cycling. Once you run out of carbs, protein is converted to glucose... that means you're losing muscle, not fat. So carb up before you ride.
The key here is metabolism maintenance. The more you carb up, the more you can ride, the faster your metabolism goes, the more you can eat without gaining weight, etc. I'd focus on being able to really spin some miles before I focused on cutting cals and burning fat. Your body will thank you for it. If your metabolism is high... you burn calories while sitting on the couch. That is your goal.
In my own training, I had made the mistake of not eating enough, and to be honest I JUST started carbing up heavily the night/morning before a ride, and its made all the difference in the world in my training. I'm adding miles, and thats the best way to lose fat.