Not too much for a natural, but it does take proper implementation to get the most of it. I am a natural, I've done the Colbert full body plan three separate times over the past 5 years, I actually went through the majority of my first contest prep on that plan! The first time I did it I wasn't in the gym too long either. I saw great growth on this plan.
When I started in the gym I was already used to fairly high volume, so the Colbert plan was kind of the next progression. I don't think it's too much, but, it will seem like if not executed properly, and if recovery isn't on point. Remember, you're not doing 46 sets every day, it's every training day which is only 3 days per week, M-W-F type deal, always a full day of rest in between. Since you're training every body part every training day, it's important to keep the following in mind:
-Make sure you're getting adequate nutrition on this plan, especially around the workout window, like Finibars, Plazma, and Mag-10. I highly recommend being in a caloric surplus while on this plan.
-Sets should not be taken to fail ever since you're working every body part every training day. Intensity should be high for sure, going hard, but don't go to fail. Always leave one or two "in the tank." Training intensity and recovery will ensure you'll grow, going to fail is a recipe for injury and imparting your CNS/recovery/gains.
-Move quickly so the workouts don't take two hours.
-Make sure to get a warm up/feeler set every time you start a new muscle group. Also will help avoid injury.
-Prioritize recovery, supplements, vitamins, sleep, etc.
-Be sure to select a good exercise selection and rotation over the three days to hit all the angles necessary.
It might take some getting used to the first week, but once you know your way around the program and exercises you should be able to get the entire thing done in 90 minutes. Another great aspect about this plan is it really eliminates the need for any excess cardio since it's a long workout. Again, but sure what your nutrition is like right now, but I highly recommend being in a caloric surplus on this plan to make the most of your gains and fuel your training.
As I've mentioned I've done this program numerous times, please post back with any further questions!