You can add a +1 button coins and occur at intervals as you want but not on days or hours when you enter Ui respectively ..
The feature is there but it has a bug so it doesn't work. It was reported several months back but never got a fix.
You can't do that exactly but what you can do is add a purchase button, a gift and make the interval 5 or 6 and in properties check the One time Purchase, so it won't appear again in the current session. if the users closes the game and open again the same day, it will still appear again one time...
