Depending on your setup, If you just connect to your NVR as a way to keep it recording your POE connected cameras or if you have it connected to router, switch and monitor times will vary.
However with that system being used with a 12v 9Ah battery if used with a normal setup with lets say 6 cameras with 5 of them being normal static and 1 Goliath type camera. Depending on the time of day/night with the specs of the UPS it would support around 1 hour of backup.. Now removing the Goliath type camera, I have more then 1 on my systems, So running only 6 normal cameras would give you about 1 and half hours of run time connected to the NVR alone. Again adding in extra things like a monitor and router will lower them times. So your NVR says without HDD it uses 15.2w, I added in what I think 2 HDD might have for total of 30w, Actual numbers could be lower or higher seeing 2 WD Hdd is 17.4w, just guessing what one might use.
NVR 30w
5 cameras 10w Could be much less just needed a number to run.
1 Large PTZ camears 25.5w
Total power for NVR and connected cameras
30+ 50+ 25.5 = 105.5W
UPS Battery 12v 9Ah = 108Wh
108Wh / 105.5W = 1.02 hours. Again with normal cameras in the day time that could be as high as 2 hours of run time give or take .. At night time with IR on the cameras that time again would be close to the 1hour..
Keep in mind that my values are high aka max of what might be. So your time most likely would be much higher run time unless you add in the Monitor and router then will be reduced per rating of the device..
Personally I use a Pure Sinewave Rack mounted UPS. I don't personally know the UPS you are looking at, Some systems with a Modified Sine Wave UPS can cause issues with your power supplies and even damage your NVR. Another issue to keep in mind is Transfer time or Switching Delay. Voltage Regulation issues with Inconsistent Voltage Output.. Electrical Noise.. Then if you were to look at some of the high end people they like to add in Compatibility with POE and while this is kind of true not as much as they like to claim. Most of it is that people when sizing the UPS look at only the device wattage and not the added in wattage of the POE cameras that would be connected to it. In my post as you can see I did add in 5 cameras even using the 6th with a PTZ camera that is rated for .at where normal POE cameras are rated only .af.. So I was trying to provide a real world idea of what the UPS you were looking at might support.. Hope that helps.