You risk not being able to fully recover between one workout and another or not being able to maintain a good level of training because you are still tired from the previous one.
Then as @HellYeah said it's up to you to decide what's right for you
@savar welcome to The Hive. The short answer to your question is "No, you can't".
There is a longer one that requires a lengthier explanation. Each program is specifically designed to trigger specific adaptations in the body which will help your fitness. Both the trigger and the adaptations are dependent on the body's homeostatic balance (i.e. its baseline fitness values or metrics) which are a host of neurobiological, biological and physiological responses. And the baseline values (or homeostatic balance) depends on the body's allostatic balance (or the complex neurobiological, biological and physiological stressors it experiences).
Each workout we publish has undergone, on average, about three month's worth of testing and refinement and each program we publish has undergone between a year and eighteen months' of testing and refinement to make sure that the ideal mix of stressors and recovery time are put together in order to trigger the adaptations necessary for your body to change and you to get fitter.
When you do two workouts in one day you are basically undercutting this logic. Depending on what you do you may be overloading your body in which case you will not get the response you need, you may be adding stressors which will not trigger the adaptations necessary (for reasons that have to do with the complexities of the trigger/adaptation response in the brain/body pathways) and you are certainly not giving yourself anywhere near sufficient recovery time and we know that the adaptations occur when the body is in recovery mode.
I hope this explanation helps expand your own awareness of how the body responds to exercise so you can better reach your fitness goals.