Google has just updated Google Now, which is now capable of providing a countdown timer to your important event. This might be reminding to brush your teeth, or a doctors appointment, or even your own wedding.
Android Police discovered the new ability of Google Now, with the countdown timers reportedly being part of your reminders. As it stands, these reminders aren't tied to the Calendar right now, so you can't add the doctors appointment into your calendar, and have Google Now remind you of it. Although, you could create a countdown timer separately.
Android Police explains: "Basically, if you have a reminder related to an event Google knows about (like Christmas, for instance), Google will pick up on that and - on your reminder card - serve you a countdown. The functionality doesn't seem to work with things like birthdays yet, so it probably won't work with any personally-connected events, but it does work with events that Google as a service recognizes, like holidays".