Hi there

, I'll try what I can to help. Will try using both types of terminology to explain as I'm unsure what you are used to. I find most of NZ uses the same words, and I'm hoping Aus does too, but just for incase I'll include USA terminology too.
So.... Do you try this on hard surfaces often?
A rebound in gym uses the floor to push you up, its not just you doing the work.
So trying it on a hard surface a lot before you can do it properly may be holding you back a bit because you first need to absorb the shock from the hard surface before going up again. If you can't practice in a gym enough, soft grass might be the next best thing?
Another reason your rebound is delayed is because your chest is still fairly low to the ground. The shoulders need to block/prop more. You are bent at about 90 degrees at the hip when your toes hit the ground, should try to be more straight than that. More of a dish/hollow shape.
Drills to help the prop/block would be doing handstand props, shoulder shrugs while doing a handstand against a wall, or.... one other thing you can try....
If you training at gym and have a soft cylinder, or maybe a small soft box? try putting it between where your hands get placed, and where your feet land. That will force you to push harder with the shoulders to try clear the object.
Hope this helps you, if there is anything I said that you don't understand then just ask
