We suggest resetting the game once you find that it takes too long to unlock the next girl. Resetting the game will reset your current progress and you will start from the beginning. However, you will also receive an in-game bonus which will make your game progress faster than before. This bonus you get depends on how far you progressed in the game. So the more girls you've unlocked the bigger the bonus.

Click the clock icon on top of the game and choose "Speed by Reset", "Reset & Collect" to reset the game and remember that anything that is purchased with diamonds (Energy/Studio/Time Warp/Outfits) will remain even after you reset the game.