Everyone is different so everyone may gain at different speeds and even benefit from different routines. What may work for one person may not work for another. Unfortunately there are not many good studies in this industry, so the results are from my own, others like members on big forums and our clients and members feedback which is all anecdotal.
For size, a general rule of thumb is 1 to 2 inches in 1 to 2 years. This may mean 2 inches in one year, or 1 inch in 2 years. This is where the need for consistency and commitment comes in as its marathon, not a sprint.
For stamina, penis enlargement is only one part of the picture, that's combined with masturbation and edging techniques. The more you work on it and practice the better you can master control.
For hardness, this is going to come down to many factors beyond PE methods alone. Main contributors will be things to do with your general health and lifestyle including nutrition, hydration, sleep, movement, mindfulness, breathing and more. Essentially, if you take care of yourself as best you can, your erections will follow suit. A lot of this content is covered along with PE specific techniques on the Total Man Video Library .