Have patience, the cards will appear when they're most useful. Also, the calendar cards don't appear when you make the appointment, it shows up to remind you and possibly give you an estimated time from where you are to the location of the appointment.

Give it time. Mine popped up 5 cards that I commonly get in Google Now on my Nexus 7.

So it's a initialization delay? If you add something in your calendar, does that pop up as a card right away?

When is the event? Reminders usually pop up the night before the event for me.

I tried to put it like 1 hour in the future, or 30 min in the future. I think I wanted to ask is, if you add an event that it should pop up now (e.g., it's in the evening, and the just added event is tomorrow), does it show up instantly or is there a delay for Google Now to find out about the event?

It tries to be predictive - if an event is added that happens too soon it won't pick up on it. Add a calendar event for tomorrow and see what happens.

Try hitting the refresh button at the bottom, that did it for me.

I did that, and re-opening the app. Still didn't work :-(