The answer that arrives after the useful moment may need more than an explanation of accuracy.

Accuracy delivered after the moment has passed solves a problem nobody still has. The decision was made without you, somebody worked around your silence, and a thorough answer arriving now lands on a situation that has already moved. Timing was part of what was being asked for, not a separate courtesy attached to it.

When you miss a window, lead with the delay rather than the content. Say what it cost them, say what you will change, and keep the explanation shorter than the apology.