How to calculate the sum of minutes in android studio

forgive the inexperience since I am new, I would like to know how I calculate the minutes better said add them to give me an hour of departure. What happens is that I want to perform an exercise of the income of patients in consultations, therefore they are asking us how long it takes patients with each doctor, entering first the time entered the consultation and then add the minutes that each patient takes with the doctor, for example, how long I stay, with a psychologist, with a dermatologist, with a general medicine, etc. and deliver the total result as the time of departure.

for example:

     package com.example.asus.crudaplicacion;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

public class IngresarDatos extends AppCompatActivity {
    EditText e1,e2,e3,e4,e5,e6;
    Button bt1;
    TextView t1;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_ingresar_datos);
        e1=(EditText) findViewById(R.id.edtHora);
        e2=(EditText)findViewById(R.id.edtPsicologo);
        e3=(EditText)findViewById(R.id.edtTrabajador);
        e4=(EditText)findViewById(R.id.edtMedico);
        e5=(EditText)findViewById(R.id.edtTraumatologo);
        e6=(EditText)findViewById(R.id.edtOtro);
        t1=(TextView)findViewById(R.id.hora);
        bt1=(Button)findViewById(R.id.btnSumar);
        ....................................

    }
}

Here I have the configuration code, but afterwards I do not know what to place, forgive the ignorance is that I am new to this.