But if the virus replicates sufficiently before chloroquine + zinc is administered then much damage is already done.

So it's a race between the virus and the "cure". Get the "cure" in quickly and the virus stops replication before much harm occurs; get the "cure" in late and the virus has run most of its course and maximal damage is done.

Also, since the viral damage opens the door to opportunistic bacterial infections (e.g., pneumonia), antibiotics may be given to prevent bacteria from taking hold.