Two of my cats have recently had UTIs (crystals). One was on 125mg. of Clavamox twice a day for 10 days, the other 62.5mg. of Clavamox twice a day for 14 days. Different vets at the clinic prescribed for the cats, thus the difference in dosage.
I'm not familiar with Zeinquin but 10 days is usually enough to eliminate the infection. If your cat is showing any signs of discomfort in urinating or inappropriate urination after 10 days more antibiotic may be needed.