Update current time and find difference

I have this function where user can update current time this.oldTime this is old date and time, 10:06 this is new time it can be 04:25. I want to find the difference how many minutes added or subtracted from old time.

 UpdateTime()
  {
    this.utcTime = new Date().toUTCString();
    this.oldTime = new Date(this.utcTime).toLocaleString('en-US', { timeZone: 'Asia/Calcutta' });
    let oldTime=this.datepipe.transform(this.oldTime, "yyyy-MM-dd HH:mm:ss"));  // 2023-04-15 08:42:12
    let userenteredTime=this.newTime;  //   10:06

}

}