^ be very careful with this state of mind. Many of my games end between 20 and 30 minutes and I consider myself a very CS focused player. As you get better at the game farming will get easier to accomplish, for you and your opponents. If you only focus on pushing lanes and ganking you're eventually going to run into players who know how to escape ganks, punish your mistakes and out farm you all at the same time.
If you instead focus on pushing your lanes, zoning, and punishing your opponents missteps I guarantee you that you'll notice you only need two or three mid game items to really start taking the win. (one example I can think of is Elise, if you just poke and farm until you have sorc shoes, haunting guise, and a giants belt you can practically run the fights, often ending the game before you finish ryleis; the same can be said for many champs on TT.)
About the original topic; early game death timers help prevent teams with dominating early comps from getting to large a lead by taking a super early turret or getting a huge level advantage.