Whenever you hear about a very tight schedule, it's because someone has ended up with more appointments in their day than is reasonable; our capacities as humans are good for socializing for hours on end every day, and not so much at physical or mental exertion. Athletes and top researchers most likely aren't engaging in this level of precision.

Basically, unless you're really ambitious about taking a "leadership" role, you aren't going to need to schedule your life at more than perhaps hourly intervals. It's still a good idea to have a little bit of scheduling to build up your day as an intentional lifestyle instead of a series of reactions(I tend to do the "calendar as to-do list" thing), but you can do so in moderation.