Not currently possible but an often requested feature, about to be requested again next month at Redmond.

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Milly Staples [MVP - Outlook]
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After furious head scratching, Goldsmack12@gmail.com asked:
| Does anyone know of a way to set the outlook work week for someone who
| works either an overnight or and varying hours depending on the day,
| but consistant from week to week (ex. Sun-Thurs 8PM-4AM or MWF
| 10-6,TTH 9-5)?