I'm doing an ELISA experiment. I washed the microtitre plate coated with antigen with PBS and BSA for each well. Should I empty the PBS/BSA from the wells and leave the empty plate until I'm ready to use it to add the antibody or should I leave the PBS/BSA in the wells and empty them just before use?

Any time that I have carried out an ELISA I have left the PBS/BSA in the wells for 1/2 - 1 hour. This step allows the BSA to bind and block no specific binding sites.