Why this works
Will It Fit? leans on one well tested idea: plan with how long things really took you, not how long they feel like they will take. Here is what that rests on, and what we will not claim.
We guess short. Our past knows better.
People underestimate how long their own tasks will take, even when similar tasks ran late before. They picture the plan and skip their own track record. In one study, asking people to tie the estimate to how long similar jobs had taken them removed the bias.
Buehler, Griffin and Ross (1994), Journal of Personality and Social Psychology 67(3), Study 4. doi.org/10.1037/0022-3514.67.3.366
Review of later work: Buehler et al. (2010), Advances in Experimental Social Psychology 43. doi.org/10.1016/s0065-2601(10)43001-4
That is the stretch factor. Each time you finish a block, you tap how long it really took. Will It Fit? keeps an average of your last ten and sizes new blocks with it, so a 30 minute guess lands as 42 if that is how you run.
Big, ugly tasks are the ones we put off
Across 691 correlations, how unpleasant a task feels, how far away its payoff is, low confidence and impulsiveness all go with putting things off. It is correlational evidence, so it shows what tends to travel together, not a single cause.
Steel (2007), Psychological Bulletin 133(1). doi.org/10.1037/0033-2909.133.1.65
So blocks come in small sizes, and anything that will not fit today can wait on the Not today shelf. The shelf is grey, never red, and it never counts.
Specific plans help more than vague ones
Across 94 tests, specific if and when plans ("when my shift ends, I will start the laundry") helped people reach their goals, with a medium to large effect. This is about specific plans, not planning in general.
Gollwitzer and Sheeran (2006), Advances in Experimental Social Psychology 38. doi.org/10.1016/s0065-2601(06)38002-1
So fixed things, like a class or a shift, sit at their real times, and everything else pours around them.
Seeing the day as a shape
Many people find it easier to see time than to read it as numbers. The evidence here is thin: no controlled trial of visual timers for ADHD was found, only single case studies. One recent abstract found that a bar that empties smoothly felt more urgent than one that drops in steps.
Kaur, Zhao and Ongchoco (2025), Journal of Vision 25(9), abstract. doi.org/10.1167/jov.25.9.2292
Single case studies: Dettmer et al. (2000). doi.org/10.1177/108835760001500307
So we say the jar is easier to see. We do not say it is proven.
Time Guess is a game
A review of 27 studies found that children and teenagers with ADHD judged durations less accurately and less consistently than their peers. Studies in adults are scarce and mixed.
Zheng et al. (2020), Journal of Attention Disorders. doi.org/10.1177/1087054720978557
Mette (2023), International Journal of Environmental Research and Public Health 20(4). doi.org/10.3390/ijerph20043098
"Time blindness" is a popular phrase, not a diagnosis. Time Guess is for fun and for a first nudge to your stretch factor. It cannot tell you anything about ADHD or any other condition.
What we will not say
- That it takes "23 minutes to refocus". The paper usually cited for it has no such figure (Mark, Gudith and Klocke 2008).
- That unfinished tasks haunt your memory. A 2025 meta-analysis found no memory advantage for unfinished tasks, though people do tend to go back to them (Ghibellini and Meier 2025).
- That streaks, scores or red overdue counts help. There are none here.