To get fast switching between two Amiga modes you have to make sure (using Indivision config tool) they use the same DVI output mode, so your monitor does not resync at switch.
I use Indivision with Dell 1708FP monitor. When changing Amiga modes involves changing output mode, the switch takes 2 to 3 seconds. It depends on monitor. If there is no output mode change, it takes about 0.5 second, which depends on Indivision.
