It is hard to know when the neomycin drops will take effect as it will depend on the severity of the infection, your immune response, and if the diagnosis was correct.
If your symptoms have not improved after one week or symptoms deteriorate you should return to the doctor. Neomycin ear drops should not be used longer than 10 days.

Neomycin ear drops are used to treat inflamed bacterial ear infections. The active ingredients are neomycin and polymyxin, antibiotics that kill bacteria, and hydrocortisone which is an anti-inflammatory corticosteroid that helps with swelling and pain. Neomycin ear drops will only relieve the symptoms of bacterial ear infections.

You should continue to use the drops. The usual adult dose is 4 drops 3 or 4 times a day. You need to lie with the affected ear upwards and once the ear drops are instilled you need to remain in that position for at least 5 minutes so the drops penetrate the ear canal. It is also important to shake the bottle before use.

For more information on Neomycin ear drops see:
https://www.drugs.com/pro/neomycin-polymyxin-hydrocortisone-ear-drops.html