[quote]Still work to be done, he is leaning back towards his heels too much.
This “leaning back” as you call it could be a pre-cursor to and facilitate opening before foot strike. I think I see a little head tilt and the cue “keep the eyes level” may be all that is needed to correct this posture change. I’d work on this first before other fixes for early rotation.
[quote]To me it still looks like he is starting to rotate the shoulders before foot plant, so his timing is not perfect by any means.
If you feel he is still opening early before foot strike- which is hard to tell from the video- you have a couple of additional choices- leave the upper body timing the same and speed up the lower half or slow down the top half.
My choice would be to move a little quicker with the lower half and get into foot strike before the upper half can begin rotation. It sounds like you’ve been this route before. Unfortunately one or two day camps are tough since timing changes can take time and feedback to master. This might be a good time to try again since you know what to look for now and the change may not feel so drastic. Moving faster has the additional benefit of generating more momentum toward the target.
To slow down the upper half work on stabilizing the glove out in front of the torso a little longer. I’m not a fan of slowing down because it creates more time for things to go wrong, especially with youth pitchers.
One final thought. Since this is a changeup it is common for everything to slow down which obviously you want to guard against. If it is a circle change then there can be a tendency to move to the glove side to help with pronation.