There is no chance to ever measure Planck lengths or Planck times. They have no experimental effects whatsoever. Are they useless concepts?
Let me assume for a while that we drop these two concepts. It would mean that we keep quantum theory and gravity separate. We drop unification. What happens? Not much. Quantum theory and particle physics remain valid. Also general relativity remains valid. We know of now experiment that requires both theories at the same time.
In practice, avoiding unification has no effect, because the standard model of particle physics and the concordance model of cosmology agree with all experiments.
So, do we need unification? My answer: yes. We need it to understand the parameters of the standard model and of the concordance model.
Do we need unification for other reasons? My answer: no. But many researchers would answer yes. They add anomalies, instabilities, fine tuning, dark matter and more reasons.
Are the Planck length and the Planck time essential for unification? My answer: just a tiny bit. Other ideas are more important. Is nature really a bowl of noodles? Is nature really a huge gut full of moving intestines? These proposals are, if they are correct, more shocking than the Planck length and the Planck time.