Attached the construction I use.
The Sapporo can fits so well it seems it was designed for this purpose. The beers all right too :)
I found it easiest to use the can opener from a swiss army knife to cut the top and bottom out of the can. The regular tin opener we have for the kitchen just made a mess of the can.
Next step is to find some metal mesh to improvise a chaff catcher for the top of the can.
Ive also got a Behmor which I use for bigger batches. The popper is great to quickly roast up some small quantities of beans.
My timings are about the same as yours. First crack around 03:00 and dump between 06:30 and 07:00. The popper makes so much noise that I only hear the 2nd crack once Ive switched it off!
I immediately dump the beans into a bean cooler, and they then take about 60 seconds to be hand warm and 90 seconds to be cold enough to pack away.