Brihat Parashara Hora Shastra
एकादिसंख्यया निघ्नं दशामानं पृथक् क्रमात् । राहुकेतुयुतानां च नवानां कालसंज्ञकम् ॥ ४९॥
If the birth is during Sandhya, then its past Ghatikas should be multiplied by 4 and the product divided by 15. The figure so arrived at in terms of years, months etc. should be multiplied by the serial number of Sūrya and the other Grahas to get the Kaal Dasha of all the nine Grahas.
english translation
ekAdisaMkhyayA nighnaM dazAmAnaM pRthak kramAt । rAhuketuyutAnAM ca navAnAM kAlasaMjJakam ॥ 49॥
hk transliteration by Sanscript