Conventional cooking wisdom tells us to soak grains like barley or steel-cut oats overnight to cook them more quickly and produce better results. Serious Eats' tests, however, suggest you can skip that step and cook them straight from dry.
Daniel Gritzer cooked side-by-side grains that were unsoaked, ones that were soaked overnight, and ones soaked overnight with salt. His tests included whole-grain barley, pearl barley and steel-cut oatmeal. He concludes:
Well, mainly that soaking grains isn't necessarily going to speed things up, and salting doesn't seem to make a (salt-)lick of difference. And when soaking does help, as in the case of pearled barley, it doesn't always look pretty. If you don't care about appearances and are desperate to knock 15 minutes off the time it takes to cook polished grain, go for it. I, for one, will just accept my grains as they are and wait patiently for them to do their thing.
So if you forget the overnight soak, don't worry. You can still cook those grains with little detriment in terms of time or flavour. However, one reason you might want to consider soaking grains is to possibly make them more digestible. Your call.
Do I Need to Soak My Grains? [Serious Eats]