Travel Question

Upon arrival to Zihuatanejo they ask you at customs how long are you staying.
What if you don’t know that and your travel is open ended.
Is there a problem when you depart or how do you answer?

You are there with a tourist visa, yes? My layman understanding of the law is that you can stay up to six months. Tell 'em the truth that you don't know but you will be sure to obey the law and leave Mexico within the six-month time limit.