Muhūrta is the doctrine that time has qualitative texture — that certain windows favour certain actions and others disfavour them. The classical view is not deterministic ('this will guarantee success') but conditional ('this removes one class of obstruction'). Phaladīpikā Ch. 26 covers the major muhūrta categories: vivāha (marriage), gṛhārambha (laying the foundation of a house), vyavasāya (commercial venture), and yātrā (travel).
The 5-limb pañcāṅga from the Foundation path becomes the working filter: certain tithis are favourable for certain undertakings; certain nakṣatras are auspicious or restricted (Mūla and Jyeṣṭhā are restricted for marriage, for instance); certain yoga-karaṇa combinations form durmuhūrtas (inauspicious windows). The full muhūrta-tradition includes the Muhūrta-Cintāmaṇi and the Muhūrta-Mārtaṇḍa beyond Phaladīpikā and BPHS — but Ch. 26 + Ch. 90 give you the foundation.