score:7
You can find the answer in the website you linked:
The one-day card is valid on the date inscribed until the end of operating hours, the two-day card is valid on the day inscribed and the following day until the end of operating hours.
In your case you need a two-day card.
Upvote:1
Since you leave mid-day, it's surely necessary to buy a 2-day-ticket. At least here in Switzerland operating hours end, when the next day's operating hours begin. In numbers: Any ticket you buy is valid the date printed on it until 5am the next morning. For further information I'd write a mail to the tourist information website. I'm sure that they will gladly help you.