Offer a similar "budgeting" experience as YNAB, but constrained (you literally have 24 hours a day, no more, no less). Create categories and subcategories. Work - Programming, Meetings, blech; Meals - Breakfast, Lunch, Dinner, Preparation, Shopping; Kids - Transport, playing with, working with; Home - Bathroom, Kitchen, Floors, Mowing; Financial - Bills, Budgeting.
Open the app and log your time, specifying the appropriate category. Reallocate time. You wanted to spend 24 hours at the lake this month (rented a cabin, camping), but you needed to clean the gutters and forgot about it so you go to the lake later on Saturday, not first thing in the morning.
Would be able to generate reports at different levels of granularity, like a budgeting/accounting app can. Generate a daily, colored, chart so you can see where in each day you spend time (or don't for unaccounted for time) and identify trends and problems (I go to bed between 8pm and 11pm, maybe I should make that more regular).
I know I wasn't great with money until I counted every cent for a while, I wonder if the same effect could be replicated for people who don't spend their time as effectively as they'd like.