Chronophagous

chronophagous \krə-ˈnä-fə-gəs\ adjective: 1. using or taking up a great deal of time; time-consuming {chronophagous chores}, 2. wasteful of time {chronophagous tactics}

Etymology: Greek chrono-, from chronos time + -phagos, from phagein to eat

Time-consuming is fine among friends, but use chronophagous if you’re feeling pretentious.