Kimstughna is the fourth fixed karana and the only one placed at the beginning rather than the end of the sequence. It occupies position 1, the first half of tithi 1, Shukla Pratipada, which begins at the exact moment of the new moon.
Every other karana starts where the Moon has gained a further six degrees of elongation from some earlier boundary. Kimstughna starts at elongation zero, at the conjunction, and runs until the Moon has gained six degrees. It is the anchor of the whole scheme: the tithi count, the karana count and the fortnight all begin at the same instant, and Kimstughna is what occupies the first slice of it.
Its position also completes the block of fixed karanas. Shakuni at 58, Chatushpada at 59 and Naga at 60 close the waning fortnight, and Kimstughna at 1 opens the waxing one, so the four run consecutively across the new moon and no movable karana falls in that stretch of roughly two days. The reason four positions had to be taken out at all is arithmetic rather than doctrinal: sixty is not divisible by seven, but the remaining fifty six positions are exactly eight rotations of the seven movable karanas, so the cycle closes at the end of every lunation instead of running on broken into the next.
Bava takes over at position 2, and the rotation of seven then runs uninterrupted to position 57.
A karana averages 11 hours and 49 minutes and varies with the Moon's speed.