The yoga is the limb of the panchanga that has no counterpart in the sky. Nothing about the day looks different when one ends and the next begins. Where the tithi measures the Moon's separation FROM the Sun, the yoga measures the two longitudes ADDED together, and cuts the resulting circle into twenty seven equal arcs of thirteen degrees twenty minutes. Vishkambha is the arc from 0 degrees 00 minutes to 13 degrees 20 minutes of that sum. The sum climbs at roughly fourteen degrees ten minutes a day, so a yoga runs about twenty two and a half hours on average, a little shorter than a tithi, and like a tithi it can be skipped between two sunrises or carried across two of them.
The twenty seven arcs are the same width as the twenty seven nakshatras, and Vishkambha is the first arc of the grid in both schemes, which is why the two are often tabulated side by side. They are not the same thing and share nothing but their arithmetic: a nakshatra is a segment of the sky the Moon is physically standing in, while a yoga is a number derived from two positions and belongs to no part of the sky at all. Reading a yoga as a star group is the commonest confusion the term invites, and the shared name of the first position, Ashwini, is where it usually starts.
Vishkambha sits among the nine yogas classed as unfavourable. Nine of twenty seven is a third of the cycle, so an inauspicious yoga is a common event rather than a rare one, and the muhurta literature treats it accordingly: it weighs against a time without ruling it out, and is routinely overridden where the tithi, the nakshatra and the weekday agree.