A common dark pattern seen in modern mobile games is the timer. Often, you have a certain amount of "energy" that you can use to play the game. When you run out of energy, you can no longer play until this energy replenishes itself. This happens naturally over time, but you may have the opportunity to Pay To Skip
the timer and instantly replenish it. When these two patterns are combined, the player has the opportunity to spend an unlimited amount of money on the game just to keep playing through an artificially barrier.
Another common in-game timer is related to "harvesting" or "research". You may send your character off to harvest some resources, but you have to wait an arbitrary amount of time before this task is completed. This forces you to stop playing and wait for the timer to expire. Often there is a way to pay money or watch an advertisement
to accelerate or skip the timer.
Games that prevent you from playing them whenever you want are trying to get you to space out your playing throughout the day. This is a much better way for you to develop a habit of playing the game, and also a way to prevent players from reaching the end of a short game or getting burnt out on a repetitive game in a relatively short amount of time.
However it's implemented, the game is creating a negative experience for the player (not being able to play) that results in a positive outcome for the game developer (payment for skipping timers).