Gulika Kaal is the eighth part of the daytime that falls to Saturn, and it is avoided for beginning auspicious work. The part runs down the week in a simple descending order, from the 7th part on Sunday to the 1st on Saturday, and the clock time it covers is set by your local sunrise and sunset.
Gulika Kaal is one eighth of the interval between sunrise and sunset, the part that belongs to Saturn on that weekday. The weekday table is the easiest of the three day-doshas to remember because it simply counts down: the 7th part on Sunday, the 6th on Monday, the 5th on Tuesday, the 4th on Wednesday, the 3rd on Thursday, the 2nd on Friday and the 1st on Saturday.
The rule behind that table is stated in the Brihat Parashara Hora Shastra ch. 3, vv. 66 to 69. The daytime is divided into eight parts, the first goes to the lord of the weekday and the rest follow in weekday-lord order, and the eighth is left lordless. Saturn's portion is the one named Gulika, which is why Saturday, ruled by Saturn, gets the very first part of the day.
The word Gulika names two devices, and confusing them is the commonest error on this topic. Gulika Kaal, computed here, is a window of clock time: a slice of the day to avoid. Gulika or Mandi as a chart point is a longitude, the degree of the zodiac rising at one end of that same Saturn portion, and it is placed in a birth chart like a planet.
AstroZivi keeps the two apart deliberately. This page prints the time window only. The rising-degree point belongs to the birth chart surfaces, where the classical texts also disagree about which end of Saturn's portion to take, BPHS ch. 3 v. 70 giving the start of the portion and Prasna Marga ch. V its end.
BPHS names five of the eight day-parts after the planets that rule them, skipping the Moon's and Venus's portions and leaving the eighth lordless: Kala for the Sun, Mrityu for Mars, Ardhaprahara for Mercury, Yamaghantaka for Jupiter and Gulika for Saturn. Only Gulika passed into everyday almanac use, which is why it is the one printed in the daily panchang beside Rahu Kaal.
In practice the day therefore carries three widely observed exclusion windows: Rahu Kaal, Yamaganda and Gulika Kaal. Each is one of the same eight parts, they never coincide on a given weekday, and none of them is derived from your birth details. Gulika Kaal is commonly regarded as the least severe of the three, but the electional literature still treats it as a window to avoid rather than to work around.
Both are inauspicious eighth-parts of the daytime, but they fall on different parts for a given weekday and are ruled by different bodies - Gulika is Saturn's portion, Rahu Kaal is Rahu's. Gulika Kaal is generally regarded as slightly less severe, and the two never overlap on the same day.
For new beginnings it is avoided. Some traditions consider it acceptable for remedial or Saturn-related observances, but it is set aside for weddings, travel, purchases and new ventures. The classical electional texts list it as an exclusion window rather than a period with a remedy.
Divide sunrise to sunset into eight equal parts. Gulika Kaal is the 7th part on Sunday, the 6th on Monday, the 5th on Tuesday, the 4th on Wednesday, the 3rd on Thursday, the 2nd on Friday and the 1st on Saturday - a straight descending run ending with the first part of Saturday.
As a time window, yes: Gulika Kaal and Maandi Kaal are the same eighth-part of the day. As a chart factor the names are also used for the Gulika or Mandi point, which is a zodiacal longitude taken from an end of that same Saturn portion, and that is a different object from the clock window shown here.
One eighth of the day between sunrise and sunset, so about 90 minutes when the day is twelve hours long, and proportionally shorter or longer as the day shortens or lengthens through the year.
For educational purposes. Astrological interpretations are traditional and not a substitute for professional advice.