it depends on the traffic you get in order to achieve that goal, as far as i know there are 3 options
1. automated views - usually offered as a package of 4000 hours that generated using automated HR views (bots artificial views) with a long watch-time - cheap!
2. real ads views - watch-page views that usually get you normal retention average of 2-3 minutes (depends on the video content) - cost more than the option above
3. google ads - ONLY some watch time can be collected but only with https://support.google.com/google-ads/answer/2375431?hl=en.
with option 1, you can use artificial views and get the desired 4000 hours, and get accepted to the YPP, but in case of drop on those artificial views, the artificial watch-time will drop too and the channel get demonetized all of a sudden, this may raise a flag... that happened recently to many (they may refill and then you will need to re-apply...)
with option 2 you can also use a silent video or sound reduced to harvest watch time, or use a livestream with a looped video to get more watch-time per view.