Tips
Start sniping early
Don't wait for the last day. Golfers generally cancel 24 hours before their tee time. It's best to start 7 days ahead.
Snipe multiple courses
Create multiple requests across different courses for the same day and time window. One of them is bound to open up.
Have a wide window
Don't limit yourself to just a small time frame. Try to have at least a 4 hour window. i.e. 7am - 11am.