Brahma Muhurta is the window from about 96 minutes before sunrise to about 48 minutes before sunrise, so it is roughly 48 minutes long and ends while it is still dark. It is traditionally the recommended time to wake, meditate, practise yoga and study. Because it hangs off sunrise, its clock time changes with your city and with the season.
AstroZivi computes Brahma Muhurta as a fixed clock offset: it begins 96 minutes before sunrise and ends 48 minutes before sunrise, giving a window of 48 minutes that closes about three quarters of an hour before the sun appears. If sunrise in your city is 06:12, Brahma Muhurta runs 04:36 to 05:24.
That definition is the one in common use, and it is stated here because there is more than one. Reckonings that divide the night into fifteen or thirty proportional muhurtas make the window stretch and shrink with the length of the night, so a winter Brahma Muhurta would be longer than 48 minutes and a summer one shorter. This page uses the fixed 96-to-48-minute rule, and it is the same rule wherever this app prints the window.
Sunrise is not a national quantity. Across a country as wide as India the sun rises well over an hour earlier in the east than in the west on the same clock, and every place shifts by an hour or more between June and December. Brahma Muhurta simply inherits all of that, which is why a single printed time cannot be right for everyone.
This calculator resolves it by computing the true sunrise for the latitude and longitude of the city you select on the date you select, to sub-arcsecond precision, and then subtracting the two offsets. Choosing the city you are actually in, rather than the nearest large one, is worth several minutes.
The traditional recommendation is behavioural rather than predictive: rise in this window, and use it for meditation, japa, yoga and study before the day's activity begins. The quality attributed to the hour is sattvic calm, and the practices named for it are practices of attention rather than of enterprise.
This page states that recommendation and stops there. It makes no claim about what will happen to you if you keep or miss the window, and it reads nothing from your birth chart - Brahma Muhurta is the same for everyone in your city on a given morning. If you want a time chosen against your own horoscope, that is a muhurta calculation, not this one.
It begins 1 hour 36 minutes before sunrise and ends 48 minutes before sunrise, so it lasts about 48 minutes. With sunrise at 06:12 it runs 04:36 to 05:24. Because it is anchored to sunrise it depends entirely on your city and the date.
The tradition recommends the pre-dawn window for waking, meditation, japa, yoga and study, on the ground that its quality is calm and sattvic before the day's activity begins. It is a recommendation about practice, not a prediction about outcomes.
48 minutes, on the fixed definition this calculator uses - from 96 minutes before sunrise to 48 minutes before sunrise. Reckonings that divide the night into proportional muhurtas instead give a window that lengthens in winter and shortens in summer.
No. It is derived from local sunrise, so it differs across a country by as much as sunrise does, and it shifts through the year at any one place. Two cities an hour apart in sunrise have Brahma Muhurta an hour apart.
No. It needs only a date and a place. Everyone in the same city has the same Brahma Muhurta on a given morning, and no part of it is read from a horoscope.
For educational purposes. Astrological interpretations are traditional and not a substitute for professional advice.