The event will fire as soon as it can. Which means other events may pop up and block it for that turn. It could take up to like 7 turns before the gift from heaven fires off. If it doesn't fire off during a turn where there is no event then the mod isnt working. I have found that some event mods(NOT the wukindaissance debut) conflict with gifts from heaven and stops it from working. Try disabling any event mods and try it.