Impulse is a card that is not legal for Modern that lets you dig 4 cards deep into your library, You get to choose one to add to your hand and put the rest on the bottom in any order. Telling Time lets you dig three deep, put one in your hand, one on top, and one on the bottom. It allows you to set up your next draw while also putting a card you may not need to the bottom. While Serum Visions is a bit more powerful, as it costs only one mana and does something similar, Telling Time is a useful card.
With Brainstorm, Ponder, and Preordain already legal in the Pauper format, the addition of Telling Time to the all-common format is probably not that big of a deal. However, in Modern Masters 2015 limited environments, having this card at the lowest possible rarity will make it a valuable pick.