I haven't shot tons of Efke, but I have gone through 90% of a box of 8x10, with most of it shot over 1 second. These are the adjustments that I've been using.

1"=2", 2"=5", 4"=15", 8"=35", 15"=1'30", 30"=3'15", 60"=8'45"

Reciprocity adjustments are a funny thing. When I look at Francesco's technical data attached to his photo uploads I see exposure times that do not match mine. He has a much better handle on the intricacies of Efke film. You might ask him.