Durations can show in partial/fractional days based on the # of planned hours compared to the schedule assigned to the user the task/issue is assigned to (or the project schedule, based on your settings). If someone has an 8hr day as part of their user schedule, and you assign something that's 1hr, and don't touch the duration, it's a fractional part of their day. You can set the duration too to 1 day for example, but if you just let the duration automatically calculate based on planned hrs then that's why you'd see fractional days.
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@andrewhe2 Just checking in — were you able to resolve your issue? We’d love to hear how things worked out. If the suggestions above helped, marking a response as correct can guide others with similar questions. And if you found another solution, feel free to share it — your insights could really benefit the community. Thanks again for being part of the conversation!