Everything takes at least 15 minutes

In my experience no task takes less than 15 minutes.
If the very work is 30 seconds the rest is still used for administration, coffe, bathroom, email, web, usenet, talk, phone, looking out the window, rereading, testing, adjusting table, moving screen, listening to song, youtube, blog, slashdot, stretching, scratching, looking at blue led, picking nails, cleaning keyboard, preparing for home going, preparing for next day, cleaning black board, moving picture in cubicle, watering plant, removing old plant, tripping over old cofee cup, looking at bird, wondering about the name of the slow disc drive for commodore 64 and humming a song that refuses to leave the brain.

This means that a maximum of 8 things are done each day.