Time limits for assessment and reassessment define when orders can be passed, with exclusions for special proceedings and statutory delays. Time limits for completion of assessment, reassessment and recomputation are prescribed for orders under sections 143, 144 and 147, with separate periods for fresh assessments after appellate or revisional orders, transfer pricing references, search-related pending assessments, and revived proceedings. The section also excludes specified periods from limitation, including time spent in rehearing, court stays, audit directions, valuation references, settlement commission proceedings, advance ruling applications, exchange-of-information requests and search-related transfer of seized material, while preserving special deeming rules for limitation in identified cases.