I was babysitting my nephew one night while my sister and brother in law went out on a date.  I had fed him, burped him and played with him.  We were in the middle of a peek a boo game when I smelled something off.  I knew he needed his diaper changed.  I went to the hallway and grabbed his diaper bag.  Then, I took out his green changing mat.  I searched through the bag and grabbed a clean diaper, the wipes and some baby powder.  Then I grabbed my nephew and took off his pants and unsnapped his onesie.  He was awfully wriggly, so I knew I'd have to do this quickly!  I took off his dirty diaper. Then, I took out a wipe from the container and wiped his backside.  When I was sure he was clean enough, I put the clean diaper under him and sprinkled baby powder over him.  Then I secured the diaper and put his clothes back on him. 
Question: When were they finished changing the diaper?
They were finished when the baby was wearing a clean diaper.