n. An activity that uses up large amounts of time.
1997
The telephone is a major timesuck. The time-management experts say that you shouldn't reflexively answer your phone, but this requires strength of character, a steel-hardened sense of priorities, and I am, at core, hideously feeble. The worst timesucks are the human variety, rogue timesuckers moving through the office, mouths agape, poised to suck time like whales swallowing krill.
1996
Depending on how you feel about dogs, the program is either an amusing way to simulate pet ownership or the biggest timesuck since Tetris was invented.
1989 (earliest)
'The Unit' takes up time. I am getting to the age where I want to have a family. If 'The Unit' keeps on being as much of a time suck as it has been — it's an hourlong show — I am OK not to work.