Did you mean 5 secs instead of 5 minutes? I just ran a few calcs, and I figure that you would need approximately a 40# mass to sustain a 5 minute spin with a 1/4" shaft, under the best of conditions. I assumed a 1% friction factor, which is very good, even for ball bearings.
If you can even get close to 1 minute of free spin, please email me.
Kelsey
info@oscarcontrols.com