Today's Panchang — Tithi, Nakshatra & Rahu Kaal

An inauspicious period of roughly ninety minutes each day, during which new work is traditionally not begun. It is the daylight between sunrise and sunset divided into eight equal parts, with one part assigned to each weekday. Because it is a fraction of daylight, it moves through the year and differs between cities.

Almost certainly because the other site computed it for one city and showed it to the whole country. Sunrise differs by close to an hour between Kolkata and Ahmedabad, and rahu kaal is a fraction of the time between sunrise and sunset, so the two cities genuinely have different rahu kaal. This page recomputes it for the city you choose.

Tithi, the lunar day; nakshatra, the star the moon is in; yoga, from the sun and moon together; karana, half a tithi; and vara, the weekday. Panchang means "five limbs". They are read at sunrise, which is why a printed panchang and a clock can disagree about which day it is.

The day and night each split into eight parts, named by planetary lord. Amrit, Shubh and Labh are the good ones, Char is neutral and used for travel, and Rog, Kaal and Udveg are avoided. It is the quickest way to find a decent hour for something small when a full muhurat is not warranted.

The eighth of fifteen parts of the daylight, the window around local noon. It is traditionally held to be auspicious on its own without any other check, which makes it the usual answer when something has to be done today and there is no time to look further.

No, and this is the most common confusion. A tithi ends whenever the moon reaches the next twelve degrees from the sun, which can be at any hour. The panchang names the tithi running at sunrise and gives the time it ends, which is why two tithis can touch the same calendar date.