Duration of transition can not be changed

Dear community,
I try to change the duration of transition but never work. Look at preview below:

Duration can not be changed.jpg (146.3 KiB) Viewed 716 times

i drag and drop 'addictive disolve' transition, but its duration just 0.2s.
i go the the inspector and want to change the duration from there. Unfortunately i can not change duration from there.
How to change it?
Does it becouse the different framerate of my clip? my first clip is a .mp4 with 29.97 fps, the second clip .mov with 59.94 fps.
Thanks.

Solved :
This becouse there is no enough frames as 'transition handle'. Trim the first clip 1s (or whatever), so it will remain 1s as the 'transition handler'.

You can also change the default settings for things like transition duration and fade types in Preferences/User/Editing.

Thanks charles