Vimśottarī-daśā is the primary timing-system of post-classical jyotiṣa. Pārāśara's Ch. 61 declares it the daśā for the Kali-yuga: viṃśottarī-daśā proktā kalau yuge pramukha-daśā. The system is elegantly simple in concept (each nakṣatra is assigned to one of nine grahas; the natal Moon's nakṣatra-pāda gives you the starting graha and the fraction-remaining) but enormously rich in interpretive output (the 9 mahā-daśās subdivide into 81 antardaśās, which subdivide into 729 pratyantardaśās, and so on through five levels).
The 120-year cycle breaks down as: Ketu 7y · Venus 20y · Sun 6y · Moon 10y · Mars 7y · Rāhu 18y · Jupiter 16y · Saturn 19y · Mercury 17y (sum = 120). The graha that 'rules' you during a given mahā-daśā becomes the interpretive headline for that period — its bhāva-placement, kāraka-significations, and yoga-memberships colour the entire stretch. The antardaśā (level-2 sub-period) then refines the colouring.
Aṣṭottarī (108-year), Yoginī (36-year), and Kālacakra are alternatives applied in specific conditions. Aṣṭottarī is invoked when Moon meets Pārāśara's Ch. 62 conditions (Moon NOT in own sign or exalted at birth, and certain lagna-conditions hold). Yoginī is a 36-year cycle of eight Yoginīs — Maṅgalā, Piṅgalā, Dhānyā, Bhrāmarī, Bhadrikā, Ulkā, Siddhā, Saṅkaṭā. Kālacakra is the most computationally complex, with savya/apasavya alternating paths through nakṣatra-pādas.