I'm not disputing that some veteran DBs have an internal clock that gives them a strong feeling about when the ball may be in the air, but most DBs aren't just relying on "instinctual feel" to let them know when to turn for the ball. The one thing that will get a DB in serious trouble is looking back for the ball too early. It allows the receiver to get immediate separation, and often results in a big play.
Most DBs are following a receiver's eyes and body language, or have teammates and coaches yelling to them from the sideline that the ball is in flight.
I'm aware that some veteran receivers are good at disguising their facial cues when the ball is arriving, but there's also body language involved, which is harder to disguise.
It's also not pass interference to simply fail to turn around for the football, as long as no contact with the receiver is made past five yards. There is no such thing as "face guarding" in football.
Most DB coaches teach that you only look back for the ball in two cases:
1) When the DB is running stride for stride with the receiver in an interposed position between the quarterback and the receiver. For example, if he's covering a wideout on a post pattern and the WR makes his break toward the middle of the field, if the DB has inside position and is running stride for stride with the WR, it would be acceptable to look back for the ball at that point.
2) When the DB has a specific reason to believe the football is in the air and on the verge of arriving, based on an assessment of the receiver's eyes and body language, or a cue from sideline personnel that the ball is arriving.