The Unofficial Guide says to be out there 40 minutes before rope drop which seems to work perfectly, so 6:10-6:15 sounds right to me (I said right, not fun

).
If it’s any consolation, on our first trip in the modern era we walked for a 7am rope drop from the Sheraton Anaheim Park and got there around 6:15am. The problem was rope drop wasn’t until 8! That debacle pretty much directly led me to spend a lot of money on VGC DVC points. One of the best decisions I’ve ever made, the walk is much more pleasant now.