I think I may have posted the wrong string before. But, this syntax is working for me and has been for ages. If you set up SolarAltitude and use my exact inputs for ON and OFF, you will see the following:
ON:
5:30AM August 1-April 30
Sunset August 1-May 31
OFF:
Sunrise
10:30PM
Where I live, sunrise is before 5:30AM and sunset is after 10:30PM so I disable the light so it's not turning on after it should be off.