A minimum of two apps must be pinned to the Teams mobile clients (iOS and Android). If a policy has less than two apps, the mobile clients won't reflect the policy settings and instead will continue to use the existing configuration.
There's no limit on the number of pinned apps you can add to a policy.
How long does it take for policy changes to take effect?
After you edit or assign a policy, it can take a few hours for changes to take effect.
I don't see the private channel nor cannot find the channel after the team is created. Why don't I see it?
Microsoft Teams has to cache behind the scenes, and also tokens can determine how items can appear.
The best way to force the views to update is to logout and log back in.
How can I set a custom token expiry, if I can?
As of January 30, 2021 Azure is not allowing custom token expiry settings. The conditional access policies determine how the token expires are configured. This requires at least a P1 license. See the Microsoft link here.