Clearing bees from the last supers in cool weather — Porter escapes, fume board or blower, and how long does it take?

Devon, fourth year, six colonies. The last supers need to come off this week before the ivy gets going and the bees start crossing back up with it. Trouble is the weather has turned: 15-16°C by day, rain most afternoons. In August I clear with Porter escapes in a crown board and 24 hours does it. Last September in the cold I left them 48 hours and still had a few hundred bees in every super, plus wasps had found a way in above the escape. A friend has a fume board and a bottle of the almond-smelling stuff but says it needs sun to work, which we don't have. I could borrow a bee blower but I'm nervous about blasting cold bees onto wet grass. I run excluders, so no brood up there. What do you use in cool weather, and honestly how long does each take?