With Fingerprint Authentication, as long the Dynamic Signal app remains open on your phone and your session hasn't expired, you only need to use Touch ID to open the app.
How Does Fingerprint Authentication Work?
The first time you launch the Dynamic Signal app on your mobile device with Touch ID/Fingerprint Authentication enabled, you'll be asked to sign in as usual. On subsequent openings, you'll be asked for your fingerprint in order to unlock the app.
As long as your app's session is active, you'll be directed to your news feed once you've successfully authenticated your fingerprint. If your session has ended (e.g. timed out), you'll have to sign in again after unlocking the app. If you didn't pass the fingerprint authentication, you'll be asked to sign in again as well.
The length of your session is determined by your Community Manager.