You can check in as early as 24 hours and as late as 4 hours before your flight departs. Present your health documents, check in your baggage and collect your boarding pass at City Check-in. Then you can buy your bus ticket for AED 20 and head directly to Emirates Terminal 3, with regular bus departures throughout the day from 4am to 11:30pm*. When you arrive at the airport you can simply continue through to your flight.
*Bus schedule: 04:00, 07:00, 11:00, 17:00, 21:30, 23:30