With an NVR the only real choice is to go in every few months and update it if you have the older GUI (black/orange/grey) that only allows one schedule.
If you have a newer GUI (blue/white), they offer a schedule by the month, so you can get a lot closer by simply taking the average sunrise/sunset for the month.
Or some of the newer GUI has a day/night button that actually works.
Unless you purposely did something, the NVR will assign the username and password of the NVR to the camera when it first powers up.
If you cannot get into the camera, you can always factory reset the camera and let the NVR initialize it again and it will assign it the NVR user and password.