Help for timers among other things

Hello, I'm coding a tnt run like plugin, and I can't seem to figure out how to make a block change color if a player steps on it, and to make a block change color after a few seconds, and finally, to make a regular block fall like gravel.

Also, to make blocks spawn at random times 1 block above the flat landscape a player is walking on at random points around a map.

I have no code because I have no knowledge of how to do this.

Thanks,
Ark

 

Block#setType(Material)

 

Thanks, but I only want the block to change if a player walks on it, like tnt run

 

@ark9026 PlayerMoveEvent.

 

Thanks! Do you also know about the random block spawning?

Also, not working

Bump, still not answered

EDIT by Moderator: merged posts, please use the edit button instead of double posting.