My audiologist told me 6 months it's "chronic" but she's seen some people's go away after a year.
Tinnitus Talk Support Forum
Dirk De Ridder said 4 years is when it becomes "more difficult to treat" but it was an estimate, not a definitive.
Then again, Susan Shore's study group consisted of mostly people who had T for 5-10 years, and a lot of those people had major benefit. So I wouldn't worry too much about this.
Anything is possible. But yeah, it takes a lot of time.
The spikes may be temporary, but over many years, the baseline just keeps getting worse. The spikes usually go away within a few days and return within a few days.
Dirk De Ridder, the most knoweledgable scientist on Tinnitus. Or well, actually, he's a neurosurgeon. You can set up a zoom call with him through brai3n.com, but it's somewhat pricey and he might be not available at the moment. Expect a 2 week wait at the bare minimum. I've talked to him 3-4 times. There is no guarantee that anything he says will help you, but it can be informative.
@RunningMan I think that's case by case as well. My father and brother have been the same since they first got it 30 years ago.
@SarahMLFlemmer So many people seem to be having turn overs at the 12 month mark. I know not everyone but hopefully it's a turning mark for us. Who knows. I'm ending the 3 month mark. Going into the 4th month.
Chronic isn't permanent, rather it's just lasting longer than expected. The longer tinnitus persists, the less likely it is to go away, although it can disappear at any point 
@Mo8409 I think if it's mild, you're less likely to notice incremental changes over the years. For many years, I didn't think about mine getting worse, until I started noticing that I could hear it over fans, filters, white noise machines. Since I took few precautions over many years, it just slowly got worse, then the sudden larger increase in early 2022.