I know of no such timer, unless you have a virus or malware on the phone that disconnects you, or someone set up the phone to only allow for short calls. Perhaps to not waste minutes? First try starting up the phone in "Safe Mode" and make a call. If it doesn't happen, then you know it is something on the phone that is the cause and you will need to find and remove the problem. If it still happens, however, even in "Safe Mode" then it phone app, the phones hardware or something with your carrier/service provider. So start with the checking in "Safe Mode" first.
To get into "Safe Mode" please do the following.
1. First turn off the phone.
2. Next press and hold "Power" until you see the manufacturers logo on the screen, then release...