Taken from a comment off of Youtube:

The 5 MILLION mission is quite hard to achieve in one day since youtube change the way it count the view, but we can reach 5 million if unite. I want to state my opinion according research done by fans.
The rules in youtube for views already change. This may be difficult for us to reach millions in one day. I have seen other fandoms struggling day and night to pull of the views. But nothing's impossible. If we follow some fan’s research, I think we can reach the 5 millions.
fans have done some more testing to figure out how Youtube is counting views now that something has changed and view counts are slower.  It appears the biggest change is the use of a time interval in-between watching the same video again.  This "cooling off" period is what is slowing down the views.here is what they found to be the best way to get your view counted:  

1. Open browser.  Does not have to be in Incognito Mode, but makes things easier.
2.  You can be logged in to Youtube or not.  It does not matter.
3.  Watch EXO music video.  You can search for it or use a bookmark.  Either way works.  You can watch it in any video quality.  240, 360, 480, 1080, It all works. after watching it, instead of replay or refresh, close the tab and search the mv again.
4.  After watching the whole video - this is the key:  Wait at least 4 minutes before watching it again.  If you wait 5 minutes, your chances of getting your view counted increases.  If you wait less than 4 minutes before watching the MV again, your chances of getting your view counted decreases.  It may get counted, but not likely.
5.  While waiting, you can watch another video, but it is not required; just waiting.  Watching another video like will make waiting easier and more accurate.
6.  After 10 views (10 viewings of EXO MV while waiting or 5 views of EXO MV and 5 of another video) clear your browser cache and cookies.  Start again.

This "cooling off" period I believe is part of Youtube's attempt to decrease the importance of view counts and focus more on "watch time" and social activity to determine the importance of a video.  Liking, sharing, commenting and watching the whole video is also important for high view count. "cooling off" period is important. be sure our views are not wasted. Plus, we can boost the views of our other videos (i.e. Growl, MiD, Wolf, and etc.) in the meanwhile.  Anyways, that is what fans been able to determine so far.