The correct form would be "How many hours (years, months, days, minutes, seconds, etc.)?" or "How much time?"
You are correct that many is for things that can be counted (hours) and much is for things that cannot be counted (time).
Correct sentences with answers would be:
How many hours were you at the park? We were at the park for two hours
How much time did you spend at the park? We spent two hours at the park.