Yes, actually time yourself with a stopwatch.
We constantly estimate how long things will take, mostly subconsciously, and it can be eye-opening to measure how bad our estimates are.
Start by estimating how long a particular task will take. Ideally choose a task in the 0.5 to 2 hours ballpark. Then start your stopwatch and time how long you actually take.
Knowing there is a ticking clock in front of you is a good way to improve focus and avoid distractions, so the times you measure are likely to be better than normal.
Hofstadter’s Law often applies.