It’s hard for our children on the spectrum to control impulse control and emotions related to frustration. Because of this, asking them to wait is akin to asking them to stop their world from spinning. The end result? It gets frustrating quickly; they may explode, tantrum, lash out, whine, repeatedly ask, and destroy property, or any number of things to stop the waiting period.
This is why with applied behavioral analyses (ABA) your therapist teaches your child how to wait in a structured way.  First the therapist may start by reducing the waiting period to a miniscule amount of time; usually 5 seconds.
The therapist will hold a toy, and when the child asks for it, they will say wait, and count to 5. If the child can wait those 5 seconds, great! They receive the toy and all is good with the world again. If this happens regularly, the time will increase from 5 seconds to 10 and so forth.
But if your child throws themselves into ‘negative’ behaviors, the therapist will stop the program until the child has calmed down, and try again. If the child continues to engage in problem behavior that’s no issue! The therapist will simply stop trying and move the situation to something else.
As long as the adults teach the child to wait, eventually this hard lesson will sink in, tolerance for this situation will be built, and you will have a child able to wait. Teaching a child how to wait has so many long term benefits. As an adult we have to wait for many things, lines in stores, for a package to arrive, for somebody to finish using what we need, etc. If an adult couldn’t wait it would severely impact their relationships and happiness later on. Which is why therapies like ABA are so important.