Best time to post
The best time to post is the hour your own followers are most likely to be on Instagram, which is specific to your account.
What it does not tell you
Every published list of best times is an average across accounts that are not yours, in timezones that may not be yours, and following it is how a whole niche ends up posting at the same hour. Your own answer is knowable: Instagram reports when your followers are active, by day and by hour, and ninety days of that is enough to see a pattern. The pattern is usually less dramatic than the guides suggest, and knowing that is itself worth something.
Related reading on this site: Posting times by niche
Now the harder question. What do yours say?
Ask Synclify in the same plain words and it reads your own account. Every dashboard and chart in it is free to use on every plan.
Cancel any time. Every dashboard and report is free to open.