There is no universal schedule
Feira da Madrugada is often used as a broad name for early-hour shopping in Brás. Street retail, stalls and commercial complexes may operate differently. A single search result should not be treated as a guaranteed opening time for every shop.
Check exactly where you are going
Identify the shopping center, stall or street, then look up its official channels and the individual store's hours. Verify again close to your visit, particularly on weekends or holidays.
Remember transport and arrival rules
Check whether your intended metro or train service is running. Shopping early does not override your Airbnb check-in time.
Sources and verification
Check current opening hours, fares and other details with official sources before traveling