Marriage-analysis is one of the most-requested categories in classical jyotiṣa practice and also one of the most ethically sensitive. Pārāśara's framework is multi-layered: (1) the 7th bhāva of the rāśi-cakra signifies the spouse-house; (2) the navāṃśa (D9) is the dedicated marriage-varga (BPHS Ch. 54 says navāṃśa-kuṇḍalī vivāhe pramukhaṃ sthānam aśnute — 'the navāṃśa holds the primary place in marriage analysis'); (3) the dāra-kāraka in Jaimini's system, and Venus as natural kāraka-of-spouse in Pārāśara's system, give kāraka-level inputs.
Aṣṭakūṭa is the eight-fold compatibility check performed between two charts before marriage. The eight factors (varṇa, vaśya, tārā, yoni, graha-maitrī, gaṇa, bhakūṭa, nāḍī) carry total weight 36, and a sum of 18+ is considered classical 'sufficient'. The eight factors are NOT equal-weighted; some carry 1 point, others 8. /ashtakoot computes this.
Antardaśā-timing (Ch. 71) gives the year-to-month resolution. The classical signal: when the mahā-daśā or antardaśā lord is the dāra-kāraka, the 7th-lord, Venus, or a graha in the 7th house, marriage-related events become more probable in that sub-period. Note the language — 'more probable in classical interpretive practice,' NOT 'will definitely happen'. This is interpretive astrology, not deterministic prophecy.