From the Ascendant and the Debilitated Signs of the Planets

Whatever results have been described regarding the combinations of movable and fixed planets original: "charasvabhava"; referring to the classification of zodiac signs as movable, fixed, or dual are rendered fruitless if the planets are weak. If the lord of the planetary period Dasha: a period of time in a person's life ruled by a specific planet is associated with an enemy or is a malefic a planet that naturally causes harm, such as Saturn or Mars, that period specifically brings about misfortune. However, if at the time of the king's decree referring to the moment of calculation or a specific royal directive the planet is strong, in its own sign, or aspected by a benefic friend, it yields good results. || 5 ||

This refers to the time of entry into the sub-period Antardasha: a minor period nested within a major Dasha period of the root period. Now, in this context, having spoken of the full and medium results of the Eight-fold Division Ashtakavarga: a system of points used to determine the strength of planets relative to each other, the text describes seven types of undesirable outcomes. The full auspicious result of a planet's Eight-fold Division occurs when it is in the 3rd, 6th, 10th, or 11th houses the Upachaya or "improving" houses, or in its own sign, its sign of exaltation, or a friend's sign, or situated in a trine. If the opposite occurs, the result is medium or bad. For one who has gone to an unfavorable state, the result is undesirable, involving the threat of death or weapons, or is very meager. 2
The malefics in the 6th and 11th houses take away [evil]
For a planet in its own sign, the strength known in the Vedas is not diminished. || 6 || This means one should declare the results after knowing the strength or weakness. 4.

For a planet in an "improving" house Upachaya that is debilitated or in the 12th house, the auspicious result is medium, and the bad result is slightly less. For a planet not in an "improving" house, the auspicious result is full and the bad result is medium. In the six-fold strength of planets Shadbala, if the strength is full, the result is full; if small, it is less; and if the planet is combust too close to the sun, it is understood that there is no result at all. || 6 ||

Now, regarding the commencement of a planetary period, the standards of time such as Solar and others are considered.
From the book

In the chapter on Measurements in the Compendium of Astrology original: "Jyotirnibandha": || Kalpa || There are nine measurements of time: Divine, Brahma, Manu, Ancestral, Solar, Civil, Sidereal, Lunar, and Pishacha. || 1 || Narada says: All movements of the planets are calculated by Solar time. The determination of age and the gestation of women are calculated by Civil time original: "Savana"; a day measured from sunrise to sunrise alone. || 2 ||