No, digging the holes ahead of time is actually the best practice. If you're having a dry season it can also be good preparation to fill those holes with water at least once to saturate the surrounding soil so that the new trees are encouraged to spread their roots faster.
As already said, pre digging can actually have benefits. Please pre dig your holes, it is a great plan.
"Where will you drive your own picket stake? Where will you choose to make your stand? Give me a threshold, a specific point at which you will finally stop running, at which you will finally fight back." (Derrick Jensen)
You know it is dark times when the trees riot. I think this tiny ad is their leader: