I Was Told To Have My Second Infusion In Exactly

I was told to have my second infusion in exactly 6 months. I am ready to do that on Friday. Yesterday afternoon I got a call telling me to wait three days because the center was busy and that it wouldn't cause any problem. Is this true? Was the physician correct in telling me to keep this appointment or the clerical staff that called for a reschedule? I know this drug can be dangerous and am not comfortable with what is happening. Is it really irrelevant when I have then next shot?