How long does it take for a new version of an app to reach users?
I guess it depends on how the developer targets the audience .  If the developer chooses to do a staged rollout 


  You can release an app update to production using a staged rollout. With a staged rollout, your update reaches only a percentage of your users, which you can increase over time.


(Emphasis Supplied)

For more details see the link

It's best to contact the developer and check