@Juliana.Rivers - steel cut oats, rolled oats and the instant kind all started from the same oat but were processed differently (more processing in the rolled oats and even more in the instant kind), and the more processed the oats are the cooking time will be less ... here is an excerpt I copied from the Internet explains the different kinds you can buy.
The purists say steel cut are best for you because they are the least processed
Who knew that something as simple as porridge could be so co complicated!
Steel-Cut Oats - We get steel-cut oats when the whole groat is split into several pieces. Simmered with water, steel-cut oats retain much of their shape and make a chewy, nutty-tasting porridge.
Rolled Oats - Whole grains of oats can also be steamed to make them soft and pliable, and then pressed between rollers and dried. The resulting "rolled oats" re-absorb water and cook much more quickly than whole groats or steel-cut oats. When a recipe calls for "rolled oats" or the packaging mentions it, they generally mean the thickest rolled oat, which retains its shape fairly well during cooking.
Old-Fashioned Oats - The source of much confusion, old-fashioned oats are actually the same as rolled oats. You'll usually see them called "Old-Fashioned Rolled Oats" on packaging.
Quick or Quick-Cooking Oats - These are oats that have been pressed slightly thinner than rolled oats. They cook more quickly, but retain less of their texture.
Instant Oats - Pressed even thinner than quick oats, instant oats oats often break into a coarse powder. They cook the quickest of all and make a very soft and uniform mush (erm...for lack of a better description).
Edited to add the link
http://www.thekitchn.com/whats-the-diff ... cut-138355