Thank you very much for your instructive returns & suggestions !
The countdown would be a great addition indeed, but I think this issue is very specific to each level, considering the initial position of the ball is always the same atm. Perhaps for each specific level, I can place the blue ball departure at -90° or -180° angle from where you are supposed to go, so there will be enough time (90 -> 1s or 180 -> 2s) to anticipate the first movement. What do you think ?
I agree about more in-between levels, to "teach" how to beat some obstacles with very easy examples.
I'm glad you appreciated the grid, that was the goal :)