Coin Boost is a kind of Buff.

When Coin Boost is activated,
the amount of coins getting from the slot machine is increased by 30%.

If you use 100 Gems, Coin Boost is activated for 180 Min.
If you watch AD, Coin Boost is activated for 15 Min.
And you can watch AD 5 times a day.(Reset on 00:00 (UTC-0))

You can extend the duration of Coin Boost as you use gems.