You can. Thermal reads heat, not light, so the Ocelot 640 works in full daylight as well as at night. Many hunters zero in daylight and use the scope to spot animals lying in shade or cover on warm afternoons. Just avoid pointing the lens straight at the sun.
PARD packs a lot into a compact scope, and the Ocelot 640 is a good example. You get a 640x512 sensor at 20mK or better, a rangefinder tied to a ballistic calculator, and five zero profiles. Warranty work goes through PARD, and we help you reach them if anything comes up.
Many states ban thermal and other night optics for deer to keep deer hunting a daylight, fair-chase pursuit. The rules are set state by state, and some allow thermal only for hogs and predators. Read your state's current regulations before you take the Ocelot 640 out during deer season.