I’d also suggest holding the bottom position for time. I can’t overstate how important it is to be comfortable in that position. I’ve done full pistols with nearly 50% of my bodyweight in additional weight, and I still think that the combination of those two isometric exercises are among, if not, the best exercises to familiarize yourself with the pistol. Not only do they provide time under tension, but more time at the most difficult points of a movement is crucial in allowing your nervous system to adapt to the muscular activation necessary for the positions. The one leg wall sit gives you strength to press up, but also teaches you hip and leg alignment and core activation necessary to keep your form through the sticking point of the movement. Holding the bottom gives you the mobility in the hips, hamstrings, and ankles to maintain the position, but it also engages your hamstrings and calves in pulling your weight forward and your hip flexors and quads in holding the free leg up and straight out. So you see, this time gives you the opportunity to focus more on the strictness of your form while your neuvous system adapts.