My cat has ear mites, and an hour ago I just used...?

Sentry HC Ear Mite Free brand ear mite medicine. I've read reviews saying this brand does not work at all and I'd have to agree with them. I just got home from the store with some Hartz brand ear mite medicine and have been told by a few people that it worked for their cat almost instantly. I want to try it as soon as possible but I don't know if I should wait (like it might be too much or hurt my cat). Would using both brands basically at once be bad, or should I just wait until tomorrow?