I've been calling CQ on 6 meters ritualistically during the evenings on 50.4 (and lower on occasions) for 30 minutes to one hour--I even monitor longer as I work in the office. I typically look north and north west from central Florida but rotate the beam around and call CQ in various directions. I have yet to hear any activity, but I got excited when someone tuned up on 50.4 it was a strong signal--no audio. Well, my excitement was short lived.
I'll remain persistent... hopefully I'll make my first 6 meter AM contact in the next year!
AM VHF definitely requires patience and knowing band conditions.