The very fact that it is a tens-gigabit-per-second connection in an environment full of RF noise (we all love our high powered switching power supplies) makes it hard to get a reliable signal instantly. Still shouldn't take longer than a few hundred ms though (worst case).
The pretty generic TV I use a a monitor apparently keeps the links up with its three inputs, at least for a while after recent use, so switching between two powered computers is quick, about half a second. I started using that rather than a KVM since the KVM caused a retrain, adding several seconds to switching.
The very fact that it is a tens-gigabit-per-second connection in an environment full of RF noise (we all love our high powered switching power supplies) makes it hard to get a reliable signal instantly. Still shouldn't take longer than a few hundred ms though (worst case).