Can I refuse unusual hours for someone with health condition?

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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?

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OP has already said work from home is not possible so coming in later after doing some work at home will not work.

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Thanks. There is literally nothing happening before 9am, certainly the minimal admin associated with the role won't take anywhere like that long. All clients UK and the services she will help them use don't start up until 9. I've been wracking my brains but can't make it work so will see about the access scheme.