The AGM Global Vision Varmint LRF 2.5-32x50mm Thermal Imaging Rifle Scope will work in both day and night. However, during the day, it will be harder to identify or spot whatever you are looking for due to the fact that there will be a lot of heat interference from the sun.
I used mine calling coyotes during the bright sunshine day. It’s also 0° and the yote stuck out real good. Got him at 300 yards.