Narada Purana (Jyotisha Selections) · by Vyasa
Chapter 6 · Calendar, Muhurta Elements
कालमानं मुहूर्ताङ्गानि च
क्षणसंज्ञास्तदर्द्धानि तासामर्द्धप्रमाणतः ।रविः स्थिरश्चरश्चंद्रः क्रूरो वक्रोखिलो बुधः ॥ १५६ ॥
In the full Narada Purana (Purva Bhaga) this is chapter 56, verse 156.
These are named kshanas (short moments). Their halves are of half that measure. The Sun is fixed, the Moon movable, Mars cruel, Mercury mixed.
Simple meaning: 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.
ऋक्षेशे कांतिभाग्भौमे व्याधि सौभाग्यमिंदुजे ।
An oil massage may give beauty on Monday, illness on Tuesday, loss on Friday, prosperity on Saturday.
लंकोदयात्स्याद्वारादिस्तस्मादूर्ध्वमधोऽपिवा ।
The weekday begins at sunrise in Lanka. Elsewhere it starts later or earlier by a set amount.