Cooldown of 86,000 s (at sandbox testing)

[hsteam]

Hero testing

"No Cooldowns" OFF
Buy Refresher
Use ability
Use Refresher
Refresher CD is at 300 s
Sell Refresher
"No Cooldowns" ON
Buy Refresher, still has CD when it was sold
"No Cooldowns" OFF
Enjoy the Refresher with 85,000 second CD

Even if you select "No Cooldowns" ON you still have a CD of 300s.