Narada Purana (Jyotisha Selections) · by Vyasa
Chapter 6 · Calendar, Muhurta Elements
कालमानं मुहूर्ताङ्गानि च
तिथिर्वारत्रये त्वेका ह्यधिका द्वे च निंदिते ।सूर्यास्तमनपर्यंतं यस्मिन्वारे तु या तिथिः ॥ १५४ ॥
In the full Narada Purana (Purva Bhaga) this is chapter 56, verse 154.
When one tithi (moon day) lasts over three weekdays, that is an extra one. Both are condemned. A tithi that is present on a weekday until sunset ...
Simple meaning: One moon day over three weekdays is an extra moon day. Both the lost and the extra are condemned.
विद्यते सा त्वखंडा स्यान्यूना चेत्खंडसंज्ञिता ।
A moon day lasting to sunset is whole, a shorter one partial. Each moon day splits into fifteen named parts.
क्षणसंज्ञास्तदर्द्धानि तासामर्द्धप्रमाणतः ।
Those fifteen parts are called kshanas. The Sun is fixed, the Moon movable, Mars cruel and Mercury mixed.
लघुरीज्यो मृदुः शुक्रस्त्रीक्ष्णो दिनकरात्मजः ।
Jupiter is light, Venus soft and Saturn sharp. An oil massage on a Sunday can bring trouble.