On Codex Version 188.8.131.524, the time interval before the device goes to light sleep or powers off is stored in
... IdleSuspendDelay=1200000 ... SuspendPowerOffDelay=43200000 ...
If the device is just updated, the configuration lines might not exist. In that case, go to settings → power and disable then re-enable both Auto Sleep and Auto Power off. Both numbers are in milliseconds (i.e 1200000ms = 1200 seconds = 20 minutes). Restart the device (or the xochitl service) after changing the number.