I've just made a conditional offer to someone who has declared a chronic health condition. She has asked to do a shift schedule which is at odds with the way we work (starting and finishing much earlier - 2 hours- than everyone else so she can avoid busy period on trains). Unfortunately I can't make this fit as there is no work early in the day and her leaving early will mean the test of the team have to pick up her work during the busiest period. How obliged am I to agree this?