A 15 minute timer is usually good for most things. I either get done what I need to, or am so in the zone I want to keep going even after the timer goes off.
I never have any idea how much time has passed. Also useful for something that can go on indefinitely like trying to pick a movie - at the end of ten minutes a decision must be made.
Dude walked e-v-e-r-y street in NYC over the course of years. Did little increments each day. Wrote about all sorts of random things relating to the city as he went along.
There's a great segment about his obsession with barbershops/salons incorporating the letter "z" into the name of their shop eg Royal Cutz VIP