As of June 2, 2016 Instagram is changing the way of showing posts in their feed. Now, on the beginning there are going to be the posts from the people you mostly comment and like pictures with. It is done according the time you spend on their profile, even if they are in a different time zone.
Don’t ever again miss the important posts from your close friends and family, this update will surely improve the post scheduling for the most important news added to the homepage timeline.
If you don’t really understand how this new stuff work, you can visit their help center about this manner: https://help.instagram.com/1617763228546325