Dear Mac, you can add 1% of Tween 20 to the culture medium, after inoculation, keep the plate at 4 oC for 4 hrs to allow pre-diffusion of the antimicrobial agent. Thereafter, put the plates in the incubator.
Haytham answer is ok. Tween acts like a detergent and emulsifiant and the temperature of 4 oC stops the bacterial growth until the antimicrobial agent diffuses in the agar.
usually after disk deposition all protocols define an incubation at 4°C for at least 2 h. I always had good results in particular assaying hydrophilic molecules against bacteria.
However, if your target are fungi, the pre-incubation at 4°C could be useless.
usually after disk deposition, keep the plate at 4°C for 2-3hrs to stop the bacterial growth and to allow pre-diffusion of the antimicrobial agent, . Thereafter, put the plates in the incubator at ideal temperature for the target germ. I always had good results.