ثَلَاثَةُ أَوْقَاتٍ لَا يَصِحُّ فِيهَا شَيْءٌ مِنَ الْفَرَائِضِ وَالْوَاجِبَاتِ الَّتِي لَزِمَتْ فِي الذِّمَّةِ قَبْلَ دُخُولِهَا: عِنْدَ طُلُوعِ الشَّمْسِ ... وَعِنْدَ اسْتِوَائِهَا ... وَعِنْدَ اصْفِرَارِهَا
The three windows are: sunrise until the sun has risen; the sun's zenith until it begins to decline; and yellowing of the sun until sunset. The wording concerns Fard/Wajib acts that were already binding before these windows began.