Despite what is said about daylight use they are certainly not ideal in bright sunlight, but then it is primarily a night vision scope. I found I could zero it at 100 yards but I did it either late in the evening or on a really cloudy day. Big sheet of white paper with a substantial black dot in the centre. You should be able to focus in on that. Like all NV units take a bit of time focussing it in as well as you can.
If you have access to a ballistic chart you will find the first "zero" point and that being closer will be easier to see, get it on that and then move out to 100.
I suspect you will shoot most of your foxes withibn 150 yards, the Photon is spot on at that sort of distance.