AVD Session Host EXPIRED_MACHINE_TOKEN Lifetime

Hello,

I have some AVD Session Hosts wich are unable to unable to register in the AVD Hostpool because they where turned off for „some“ time. 

I am able to reactivate and reregister those clients if I change the registry here HKLM\SOFTWARE\Microsoft\RDInfraAgent.
Adding a new Registration Token and setting the IsRegistered Key to 0

What I would like to know is: How long is the Lifetime of the Machine Token? After how much time does a session host need to be re-registered in a host pool, if it is turned off?
I cannot find this information online and would therefore be grateful if someone has more information here.