After purchasing tickets in advance, do I have to enter on the specified date? What does "分级" mean?

If the ticket you book is for a specific day, you can only enter the park on that day. The grading means that different dates have different prices.
The fares are divided into four levels ABCD, and the fares are different on different dates.
If the ticket you book is for a specific day, you can only enter the park on that day. The grading means that different dates have different prices.
The fares are divided into four levels ABCD, and the fares are different on different dates.