Sorry, I’m not at all into biology so I didn’t know how to express it.
I just meant that over the course of 72 hours, the speed at which the Petri dish with the less-effective antibiotic was filling up seemed to lag behind the control by about 24 hours. At 72 hours both were “full” regardless.
Please give more details, because I've done antibiotic susceptibility tests for 20 years and I'm not aware of any control used like that.