Hello!
Sadly #PB_Entity_DeactivationTime returns Bullet's internal counter of milliseconds (live!) up to around 2000 at which it sets the sleep mode. It's not as the manual states "Time to wait (in milliseconds) before putting the entity in sleep mode when the above conditions are met."
When you set this value you can kinda prevent an entity going to sleep (if you are fast enough to stay under 2000 so any lag ruins that) but not actually set it to any value to influence it in the way the help file suggests.
Thank you so much!