"demands time" is correct and can be used in written English.
You might use it when discussing the demands of a particular situation or task. For example, "This project is complex and demanding, it will require a lot of time to complete."
This is a wine that demands time in the cellar.
The introvert demands time for the isolation that reflection requires.
That demands time, compassion and financial support to which all are entitled, and listening by our political leaders.
He organises basketball sessions, demands time away from group-therapy to watch TV sports; it is cheerful Mac who improves the patients' morale and he even (briefly) cures the stammer of a gentle, vulnerable kid by getting him laid.
Add to this the fact that women have less money and more family and caring commitments, which prejudice their involvement in a system that demands time and financial freedom to run for office.
But I worry that the incremental needs of an always-on Web — everyone wants to know what the state of play is at any given moment — will imperil the practice of longer-form journalism, the kind that demands time, an open mind, a lot of questions and sometimes results in dead ends.
Further, research participation imposes burdens, creating additional work for researchers and demanding time and energy from participants.
It generally demands time-consuming manual work to locate the feature points on skull and face.
Various diseases like asthma, hypertension, arthritis, and migraine show circadian variation that demands time-scheduled drug release for effective drug action [ 1].
Such bonds demand time and slow down an increasingly demanding industrial process.
Last year, the Somalis here demanded time off for the Ramadan ceremony.
