The sentence you've written is very clear, but here's a version with correct grammar:
"Snowy owls are very hard to see on the white snow, so they can hunt during the day."
Explanation:
- "so they can hunt in the day" sounds better as "so they can hunt during the day."
- Also, "so hard to see on the white snow" is great! It's clear and descriptive.
Good job on your sentence!