Once a bag is fully white and at least 16-18 days old, cut away or remove the polythene; TNAU cuts round openings of 5 cm. Arrange bags on shelves or hang them with 15-20 cm between each so air reaches every surface.
The folder says small buds, called pinheads, appear about a week after opening and reach full size in 4-5 more days. TNAU reports pinheads in 2-3 days and harvest 4 days later; climate and species explain the gap, so record your own.