The best time can vary based on different factors. Firstly, consider the demographics of your followers. Younger audiences might be more active late at night, say around 10 - 11 pm. Secondly, look at the type of content. If it's related to fitness, early morning (around 6 - 7 am) could be good as some people check their phones before their workout. But in general, weekdays from 5 - 7 pm are also quite popular as it's the time when people are winding down from work or school and are looking for some entertainment on their Instagram.
Well, it really depends on your target audience. If your followers are mainly in a different time zone, you need to adjust accordingly. For example, if you have a lot of followers in Europe and you're in the US, posting in the early afternoon your time (which would be evening in Europe) might be a good idea. Also, weekends tend to have more engagement as people have more free time to look at stories.