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.