Would you care to elaborate on your statement?
What issue are you having exactly with the timeout?
How do you know its an issue, and not by design?
From Apple's iOS security guide:
You can always use your passcode instead of Touch ID or Face ID, and it’s still required under the following circumstances:
• The device has just been turned on or restarted.
• The device hasn’t been unlocked for more than 48 hours.
• The passcode hasn’t been used to unlock the device in the last 156 hours (six and a half days) and Face ID hasn’t unlocked the device in the last 4 hours.
• The device has received a remote lock command.
• After five unsuccessful attempts to match.
• After initiating power off/Emergency SOS. When Touch ID or Face ID is enabled, the device immediately locks when the side button is pressed, and the device locks every time it goes to sleep. Touch ID and Face ID require a successful match—or optionally the passcode—at every wake.