I fly to/from Vancouver quite a bit and have taken the 6:00am flight several times. A couple things you need to know:

- Online checkin: make sure you print boarding passes or have the app on your phone before you go. You can go straight to security behind the Delta counter if you dont need to check bags.

- Skytrain won't get you there early enough for a 6:00am flight. Just take a taxi from your hotel. It will be about $28 CAD. Leave at 3:45 or 4:00am you will be there in 25 minutes.

- Global Entry: definitely go in the GE line for security. The signs will say "Nexus" but they also take GE.

- US Immigrations dont open until 4:30am. This is the choke point in the whole process. Make sure you are line when they open.

- Tim Hortons: make a bee line for Timmies after you pass through US immigrations. The line for your coffee can be quite long!

Your airfare is an absolutely fantastic price by the way. It's half what I normally pay. Congrats on getting a good deal!