The way in-game menu works is, take a snapshot of scene map, set it up as a still picture background of scene menu.
So a small "fade-in" time is needed in between scene change.
You can easily change the fade in time between scenes in the scene classes in your script editor, you will have to change each one of them since the transition fade works both side for both scenes in transition.
change:
def transition_speed
return 10 #or any numbers here
end
into:
Code:
def transition_speed
return 0
end