Frequently we, here, plan your final level based on your estimate for a point 1hr 10 minutes from the end of our airspace. You may be cleared to that level, then get stopped on the way up due to a crossing conflict, which cannot be planned for as it's departure time will not be known until it actually departs, 10 minutes from the cross. If it departs plus or minus 4 minutes from planned, will determine whether it conflicts.
So to answer your question; we may be planning the big picture on a grand scale, but the small picture is a minute to minute affair.
Ever seen the guy juggle the bowling ball, the ping-pong ball and the apple, biting the apple along the way?