Hi Dan. Uncomplicated ear infections typically take a week or two to improve with treatment. Tinnitus can take much longer, weeks to 2 months. If it is improving slowly, it likely will resolve in this timeframe. If it is slowly worsening, either in frequency or severity, there may be something else going on and you should have it evaluated again. It is unusual for it to become permanent, but you would certainly want to see an ENT if your doctor felt it was lasting too long or progressing.
An ear infection can cause subtle hearing loss on the affected side. This is typically in the high frequency range. When this happens, the brain may try to fill in that lost range with nonsense noises in a similar frequency (e.g ringing or buzzing or humming). This is one possible explanation. Another would be that the acoustic nerve is irritated or inflammed by the infectious process. Either way, this affect would not be expected to go away as quickly as the infection because nerves are involved and they repair and regenerate much more slowly. When it does go away, it often does so as suddenly and mysteriously as it started.