Zmanim

Zmanim (זמנים) means 'times' in Hebrew and refers to the halachic times for Jewish prayers and religious observances. These times are calculated based on the position of the sun and vary by location and time of year. Zmanim help determine when to pray, when Shabbat begins and ends, and other time-sensitive mitzvot.

Alot HaShachar (עלות השחר), also known as dawn, is the earliest time certain mitzvot can be performed. It occurs when the first light appears on the eastern horizon, typically about 72 minutes before sunrise. Some early morning prayers and blessings can be recited starting from this time.

The Shema must be recited before 'Sof Zman Shema' (סוף זמן שמע), which is calculated as the end of the first third of the day. According to the Vilna Gaon (GRA), this is calculated from sunrise to sunset. According to the Magen Avraham, it's calculated from Alot HaShachar to Tzeit HaKochavim. Most communities follow the GRA's calculation.

Mincha (afternoon prayer) can be prayed starting from 'Mincha Gedolah' (מנחה גדולה), which is 30 minutes after halachic midday (Chatzot). However, the preferred time is 'Mincha Ketanah' (מנחה קטנה), which begins 2.5 halachic hours before sunset.

Plag HaMincha (פלג המנחה) means 'half of Mincha' and occurs 1.25 halachic hours before sunset. Some communities use this time as an early start for Maariv (evening prayer) and for accepting Shabbat early. It's an important halachic boundary between day and evening.