I can't find 'Darbar' listed at my favorite cinema:

As soon as the cinemas you wish to book at, update their schedules, it'll appear on the portal. Being online ticketing aggregates, the cinema has sole control over the ticketing inventory.

I can see 'Darbar' listed, but I can't find the date I wish to book for:

Updating the date-wise schedule is entirely a cinema's call. Usually, cinemas update their ticketing schedule 2/3 days from the date of the show. As soon as the schedules are online, you'll be able to grab the tickets with us.

Can you please tell me when the tickets are available?

You need not worry, let the app be your friend. You can simply tap the Interested button. Once it turns green, you'll be notified when the tickets for 'Darbar' are live. Just go to the Darbar listing page to do so. Just make sure you've installed the app and are signed in with the notifications turned on.