Again, the racquet is heading to contact just before the flip even happens.
“Flip” by definition is quite significant turn. So that is going from tip pointing to one side to tip pointing to other side. I believe it’s not what actually happens in one move in modern forehand. I also prefer the term “swivel” as introduced by Chuk Tomlin
@5263.
So again, I’m quite sure they first swivel to enter the slot, together with drop, and then they proceed to major acceleration, where torso rotates rapidly, arm gets carried along, and racquet head achieves maximum lag.
For sure good players connect it all together, the only stop/slow down may occur at the top of takeback — arm and racquet far back and high, before the drop. Then every phase is smoothly sequencing one another, and that’s what made early observers call it “flip” as one single motion, coming from pat-the-dog (or whatever similar motion) into full lag/lay back — that famous Fed/Nadal pictures.
There’s a clear benefit of distinguishing drop, entering the slow with swivel, and major acceleration phase, when learning/correcting technique. Even if further on you’ll be perceiving it as some united motion, just drop and swing…
For me right now, there’s also much sense in “setting the blade” idea by
@5263, which is strongly related to understanding dynamic slot. It allows to vary how thin or not the contact will be, shape and height of trajectory, keeping in mind court position (closer or farther back, angles) and intention: dip it against net rusher or send high and heavy against a baseliner, for example.