Call Timer for Oppo can make your phone automatically hang up when your call reaches a configurable predefined time.
Why it is needed? Many network carriers or telecom services offer free calls for first 5, 10, 20, xx minutes. If you don’t want to monitoring the elapsed time and manually hang-up the call while talking, then you can have this application do it for you.
NOTICE

• OPPO phones:
  For Color OS 3.0, 3.1 phones such as Oppo F3, F3 plus, F1s:
  + Go to Security Center → Privacy permissions → Startup Manager. Then turn on Call Timer to allow it startup in background.
  + Go to Batery → Batery optimization → Call Timer. Then choose "Do not optimize".
  + Go to Batery → Energy Saver → Call Timer. Then disable "Free when in background" and Automatically optimize when an Abnormally is detected".
  For Oppo phones with Color OS 2.1:
  + Go to Home → Settings → Application Management → Running apps. Lock the app.
  + Find item Data Saving (either in Security center or in Settings): If enable then add Call Timer to list of background app.
  + Find item Cleanup (either in Security center or in Settings). add Call Timer to Clean Whitelist.

• SAMSUNG phones: in some Samsung phone models such as J7, J5, J3, J2, S7, S7 edge...phone system needs to be initialized (make at least one call) before you can test Call-Timer. If you buy a new phone or you reboot your phone, please make at least one call before installing Call-Timer

• SAMSUNG GALAXY, HUAWEI, LENOVO... phones in POWER SAVING MODE: Some phones have power saving feature and this feature may interfere with Call-Timer. If that is your case, please try to reconfigure power saving feature or completely disable power saving mode.

• DUAL SIM phones: In order to keep Call-Timer working well on dual SIM phones, you need to configure default SIM card for voice calls AND make calls from that default SIM card. That can be configured via system app Settings (...SIM card).