takes 1 to 12 hours to see changes on site

i have two blogs, and i notice that when i update/edit anything on one, i can go to the site and see the changes basically immediately. however, when i edit on the other blog, i don’t see the changes right away. in fact, sometimes i have to wait several hours to see them. one time it took half a day just to see my changes.

i am new here. what is going on?