This should be pretty easy using events no?
Make a common event that works on a trigger that you have set on your map and put something like this.
Restore HP: All party +30 or whatever
wait:20 frames
Its not that hard.
If you want to use a script for the day and night then go ahead, but its prettymuch the same principal as the hp regen.
Common event set on a trigger
Wait: a bunch of frames
tint screen: afternoon color
Wait: a bunch of frames
tint screen: night color
Wait: a bunch of frames
tint screen: normal
Thats pretty much the most basic event based one i could think of off the top of my head. Scripts are nice but most of the time not really necessary.