Plus the instant that both uke and nage's tegatanas make contact for the nikkyo, uke should already be (or going) down and grimacing in pain. The more you try to get up, the more pain you experience. In the video, it looks like the nage still needs to make very large adjustments in order for the technique to work, that's why uke has a lot of time to counter.
Counters are based on errors in application, a long set-up for a technique is one such less obvious error.
A good technique application should surprise Uke with un-expected lock/throw. If Uke can forsee, he can evade your technique, this may seem far-fetched if you only practice Kata, but practicing Randori (with both partners playing at will) should provide sufficient experince.
If ones fingers are grabbed, he will most likley be Uke.