PHP's function date_sunrise allows to set the zenith angle, and then find out when the Sun crosses that angle. This way one can find out, for example, when the Sun goes above 15°.
Unfortunately, date_sunrise is deprecated since PHP 8.1.
The replacement function date_sun_info does not have this functionality. It can only tell you when the Sun passes some fixed angles (sunrise, sunset and various twilights). But it does not allow setting the zenith angle manually.
Would it be possible to include this functionality in your excellent class? you already calculate the zenith angle, so what I'm asking is doing the opposite of that - tell when the Sun is at a certain angle,