This is a weird one to intentionally obscure from the player, specifically because at any time you might wish to change up the time of day to alter anything from visibility during a mission, NPC movement or shop opening times. Fallout 3 and New Vegas had the option on a single button, but in Fallout 4 you have to find somewhere to either sit or lie down - which reconciles your waiting to most settlements. Definitely a strange decision in comparison to the last handful of titles Bethesda have put out, but at least you'll be right next to your barterer of choice once you wake up.
