It's a bug where in if after you buy cards, you go progress time by doing the card game, it doesn't unlock the sleep. To unlock the sleep, right after you buy the cards, go visit Juliet and talk to her in her room to do the gifting tutorial, then go to your room and open your wardrobe. Those two tasks will unlock sleep. I've fixed that in later versions so the sleep icon is automatically clickable but it tells you what you have left to do.