They demand detailed answers well hidden in the future before considering any action in the present.
No, we don’t know how everything will unfold. We aren’t quite sure how to perform the Avoda yet. There are many, many questions. In fact, we are certainly getting even the questions themselves wrong.
So what?!
In Shemos 10:26 Moshe explains to Pharaoh why the Hebrews need all their flocks for the Holy Day in the desert (if we take their conversation at face value, anyway):
וגם מקננו ילך עמנו לא תשאר פרסה כי ממנו נקח לעבד את ד’ אלהינו ואנחנו לא נדע מה נעבד את ד’ עד באנו שמה.
“And our cattle, too, will go with us; not a hoof will remain, for we will take from it to worship the Lord our God, and we do not know how we will worship the Lord until we arrive there.”
(Translation based on Rabbi A.J. Rosenberg.)
Why didn’t Pharoah just seize on the lack of knowledge as an excuse?
Because he wasn’t that stupid.