You've got more flexibility than a woman having to give birth in nine months if she gets pregnant in a story that lasts that long. Or, for that matter, with phases of the moon. (I still remember trying to get a good description of the first crescent moon: one chance a month, even if fortunately in the evening, and sometimes I forgot and sometimes it was cloudy.)
But I've got some characters who are getting the first inklings of twilight. (Astronomical twilight*, I suppose, if they will be able to see it clearly.) And I want them to tell some things in the time, and then be on their way. Almanacs can give me the time, but the characters will be sensitive to the point of hyper of their surroundings, and so I need to describe.
Nuisance trying to do it and get ready for work at once.
*pedant point: twilight comes in civil, the period after sunset/before sunrise where things can still be distinguished clearly; nautical, when you can still make out the horizon; and astronomical, when you can't make out the faintest visible stars.