Some proteins will precipitate rapidly in the acidic conditions of the Bradford reagent, others will not. If you can't take the reading before your protein precipitates, consider switching to a different assay, such as BCA.

If you see formation of a dye-protein precipitate, the reading is no longer valid. Either the protein concentration in your assay is way too high (deep blue color) or you wait too long before reading the absorbance of the samples after adding the Bradford reagent. Reading should take place 5-10 min after adding the reagent. Raw absorbance data should be converted into mg/ml protein based on a standard curve determined with a set of known concentrations of a standard purified protein (usually BSA)

I fully agree with Pierre. It is not recommended to wait longer else you will end up having reading of precipitate

Some proteins will precipitate rapidly in the acidic conditions of the Bradford reagent, others will not. If you can't take the reading before your protein precipitates, consider switching to a different assay, such as BCA.

BSA has hydrophobic pockets (for hormone binding, one of its functions in the blood) and hence binds more CBB than most proteins do. That makes it unsuitable as standard for the Bradford assay (other than for similar proteins). Use IgG instead.