Phrases such as practice makes perfect and if at first you don't succeed, try, try again, show a common acceptance that sometimes it takes people a while to get things.
I don't think we always give a horse the time to fathom something out, to have a 'satellite delay' and we forget that some horses have a very long distance from their brain to their feet. Sometimes we are asking then to do something that is the equal and opposite to what their mother, instinct and God will have told them to do, behaviour that they don't even have to think about, and instead to do something that requires a massive amount of concentration for them. If we could WAIT instead WEIGHT, i.e. adding more pressure, in those circumstances, we'd have horses that were more willing to try and give things ago than to worry and guess what they're being asked to do. I don't really understand why we want out horses to be sharp and therefore inaccurate.
In clicker trained work it is particularly important to wait because you are asking the horse to really think about what he is being asked to do and to be accurate about it. If the waiting seems interminable, it's probably because the shaping plan has a critical stage missing.
There are times when it isn't appropriate to wait - for example, when you set off a leading a horse and he doesn't come with you, the temptation is to turn and look to see why he hasn't come with you and to wait for him. Two things happen here - first of all you make eye contact and turn your intent towards him, which tells him to stop, and he is also moving your feet rather than you moving his.
The release of pressure or the giving of a reward should be instantaneous on seeing/ feeling what you want too. That's timing.