When I was looking for a value I could use to know a screen had been refreshed, I looked into the fade in and fade out of field screens. Seems that the fade out is longer than the fade in... (and maybe people will want to speed it up?)... Not to worry, though, I've found where the main values can be changed.
Memory:
0xCC0DD6: This seems to be a placement for the fading value.
If you see what writes to it, you can see the area of code for Fade in/out.
Fade in uses value at 0xCC0DD8. It is written to from 0x63BEC4
Fade out: Set 0x63BA48 to add ax,0002 to double the speed.
These values are to do with the field. World Map will probably use different area. Maybe someone else could look through this and see if they can expand on it?