In Chovat HaTalmidim, Reb Kalonymos Kalman outlines it clearly:
It is beneficial to write out a schedule for yourself on a sheet of paper, starting with the time you wish to get up in the morning and continuing with all your activities. Use the sheet as a reference, checking back during the day to see if you have accomplished what you set out to do. (Chapter 5)
While the rebbe's target audience for the sefer was yeshiva age students, and thus he mentions this in the context of learning sessions and finding spare time for extra sedarim, the rebbe clearly saw the value in this technique for people in all walks of life:
Whether you are in yeshiva or not, the schedule of study that you set for yourself should be followed to the minute. You should get to the point that if for some reason you are not able to complete a period of learning, you should feel pained, as if the day itself remained uncompleted....
Each day, make it a practice to check yesterday's schedule. What you did not complete yesterday, you should attempt to complete today. you should only do this, however, if you were unable to to finish because of laziness or lack of diligence. If you were thrown off schedule because of a difficult passage...then you should not force yourself to complete [what] you missed yesterday.
The whole idea of keeping to a quantitative schedule is to discipline yourself to learn crisply and without meandering. (ibid.)While it is clear that the rebbe's focus was on Torah learning, his advice can be applied to the totality of the day. The carefully mapped out day will more often than not yield far better results in accomplishment than the haphazard approach to our busy lives. Moreover, it introduces the concept of discipline into our everyday operations, which generates consistency, an important ingredient to a Torah true lifestyle.
There are varying degrees to the stricture of your structure; some people may prefer an outline as opposed to a minute-to-minute checklist. As with everything, it has to be done with a keen sense of self awareness and intellectual honesty.
This eitza also lends itself finely to the idea of cheshbon haNefesh: at the end of the day, one can refer back to his schedule and see how he did. as he starts to sort through the day's events, determining what held him back here, why he dragged his feet at that point, etc., that will aid him in recalling the particularities of the day, and his interactions with people. This segues perfectly into a real, honest soul-searching...