How long can a instagram video be?

I usually see videos that are around 30-60 seconds long.

It depends upon type of the content which you are posting on instagram. Usually for common reels the duration is almost 30 to 90 seconds. But if your content is storytelling or explanation then the duration can be increased upto 3 minutes, but if you are posting common reels like memes or other entertaining content then 30 to 90 seconds is best duration. It also depends upon you too that how quick you explain or present your content.

Instagram generally supports videos up to 3 minutes for reels now and it is depended of format.

For a regular Instagram Reel, you can currently upload videos up to 3 minutes long. Longer videos may still be uploaded in some contexts, but if your goal is reach and engagement, I’d keep Reels much shorter.