Board Thread:Game Discussion/@comment-216.57.104.1-20150603160506/@comment-26715739-20150909061517

As per SteveWaterfall it seems to be linked to whether or not there's been an update that day.

No update today = no ability to watch ads today (or get free gold in store).

If you have the time and bandwidth then doing a reinstall will also trigger the ads (but only during your first session).