Depending upon the NVR hardware some allow the system time vs camera hardware time / both. Given, you already have other higher quality cameras in use the three minutes is easy to compensate for when reviewing historic data. Lastly, I have to affirm its important to validate if this camera indeed has a RTC inside. You'll know by unplugging the camera for a few hours and than booting it back up.
Keep the NTP off and don't sync it to the computer time and observe if the date & time is some random value. If it shows the same date and time with the 1 hour 3 minute error than the camera has one even if not accurate.