red_herring The ad option can be used once per "day." For me, as the tent ad, the ad for more energy, and the ad to refresh the Last tile finder all show up at the same time (5 PM Pacific time).
When you use the Last Tile finder and then use the ad to refresh it, it resets the 24 hours you have to wait to use it again. For example, if I used the LTF at 8 AM it would show being available again at 8 AM the next day. If instead of waiting I play the ad to refresh it, at 2 PM, the timer would be reset to expire at 2 PM the next day. But the ad would become available at 5 PM, so if I wanted to use it a third time, I could either wait until 2 PM the next day or use the ad at 5 PM.
Usually, I can clear most mines without it and 1 to 2 times a day takes care of the ones where I need help.
Note for new users:, sometimes it has trouble leading you to the last tile. If it says it can't find the route, or if it gives contradictory directions (e.g. leads you through a portal and then says go back through the portal), try going to another part of the location and use it again.