I came up with 4 seconds, too. So in that 4 seconds the F16 is only going to be halfway through its tack. If I were on the smaller, more fragile boat, I don't know if I would have the courage to "bet" that:

No. 1, the F18 knows the rules
No. 2, that the F18 is anticipating that you are going to tack.
No. 3, the F18 has the time, room or crew reactions to make and execute the decision to avoid me (and how) in that period of time.

I wouldn't put my boat, and maybe my life, on the line based on assumptions.

Didn't this situation used to be called tacking too close?

Also, what if the boat behind and to windward was a Hobie 16 instead of an F18? The Hobie 16 would not even be thinking about tacking yet because he has not yet reached his layline. It might not occur to him that the F16 needs to tack.

I know, I know -- I am probably overthinking this.