"Hourglass" reminded me of Soul screamers series. Emerson see dead people, while Kaylee sense death. They both don't know what happening to them. They both end up in institution because of their abilities. Then they meet handsome boys who have similar abilities and those boys explain what is happening. 
 And also like in "Sole screamer" I liked main character. She is nice, has her own opinion about everything. But she is not perfect. 
 It's hard to write a book about time-travel. Author should think through explanations about space-time continuum, how past or future can be changed without damaging it and why in the future characters didn't know what they found out in the past, when they go there the second time after traveling back the first time (If you didn't understand what I just wrote, go check Karen 's review). She has great schemes and diagrams for explanation) 
 So the author should know every answer to every possibility in changing time. And this book was full of inaccuracy and discrepancy in this aspect. 
 Even with those shortcomings it was solid 4 stars read until the last few chapters. And then it became soap-opera. I was drowning in cheap drama. It went like this: 
 Character 1: "Give me what I want or I will hurt you!" 
 Character 2: "I don't care. You will never get it from me!" 
 Character 3: "NO! Give it to him. I love you, I can't stand you being hurt" 
 Ch. 2: "I love you too, but there are more important things" 
 Ch. 3: "But you are the love of my life!" 
 Ch. 2: "My life was empty before you showed up" 
 Ch. 3: "You are the best person I've ever known" 
 Ch. 2: "You are so beautiful, I love you. But now is time to endure pain for greater good" 
 Ch. 1: "Feel my power! PAIN!" *diabolical laugh* 
 Of course I exaggerate, but not much. What happened to these adequate characters I was reading about? 
 I will maybe try second book, but I hope that it will somehow improve.