Incubation for too short will not produce adequate signal. Incubation for too long can result in negative (unspecific) staining. Since the final result of your technique can only be determined at the end of your technique when no corrections can be made, the dilution and time of incubation for each antibody should be determined individually. In general, antibodies with known high affinity should be used at high dilution and overnight incubations. Antibodies with various affinities (polyclonal) must be experimented with to determine optimum time and dilution.