Generally, limits are seen as, well, limiting, but I'm pretty sure that's an illusion.
Limits are possibilities in disguise.
Limits allow us only a distinct set of choices, and they often force us to move faster (which, it turns out, we can do). Put a limit in place, and you create a boundary. When there's a hard stop - a limit to how much or how long or how many - you find a way to complete the tasks that matter most. You abandon that which does not serve your goals (or you risk coming up short). Nothing will sharpen your focus faster than a limit. A white page can be daunting, but a tiny scrap of napkin will house as much poetry as you can scrawl on it. Take advantage of this.
This is the blessing of structure, and it's why we get more done when we have less time to do it in. There's no time for Facebook or general aimlessness. There's no time to be existential. There is only time to get the work done.
Don't get me wrong - I love to sit and ponder, and I know how useful an empty hour is to me as a creative person. But: there's a difference between choosing to relax and simply stretching work out because you have the time to get distracted. Tiny moments add up.
But don't be mad at yourself. Just set a limit and watch the magic unfold.