I've been making these for the past couple weeks to sell at our local farmer's market. They are very popular. I've been buying plain open bearings (no shields, no lube), yesterday I grabbed a random large spinner and timed it at six minutes 40 seconds. It uses 16 7/16" steel balls for weight, the frame is laser cut acrylic. Others use nickles or quarters for weights but I weigh them on a grain scale to sort them out for balancing purposes first. Also the center bearing hole is reamed for a precise fit because a laser cut hole is not precise enough. All of them will spin for two minutes, many for three minutes or more.
I've received suggestions that I need some that are more appealing to the girls, so I am going to experiment with making them a bit more sparkly using Swarovski crystals.
Shenhui 1440x850, 130 Watt Reci Z6
Gerber Sabre 408