Google keeps adding more and more ways to add special hours to your business information. First it was via spreadsheet and the Google My Business portal and then via the apps. Now, you can add it via the "card view."
(1) In your Google My Business account, select the location for which you want to set special hours from your card view.
(2) At the top of the page, click Edit info.
(3) Scroll down to the “Special hours” section.
(3) Choose the date when special hours are in effect and enter the opening and closing times for that day. Click the box next to “Closed” to indicate that the location is closed all day. If you are open 24 hours, enter 12:00am–12:00am. If you enter closing hours past midnight, make sure to set them properly.
(4) Click Add another set to add more special hours for the location.
(5) When you’ve finished entering all of your special hours, click Save. Your special hours will appear to customers on Google only for the designated days.
Here is a picture of the card view:
Here is a picture of the edit card for special hours:
Forum discussion at Google+.