Facebook counts a video view at 3 seconds, but its monetisation tools care about 1-minute views and total minutes watched. That's why the price list has views with different watch durations: 3s, 10s, 15s, 30s, 1 min, 3 min, 5 min and 10 min.
For reach and social proof, 3-second views are plenty. If you're working towards in-stream ads eligibility, choose longer-retention views and pair them with 60K watch minutes.