The Assignment & Scheduling tab on the Job Card helps you find the right person for the job and manage their bookings:

Use the Assign dropdown to assign users to the job, or groups for group tracking:
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The Schedule button will open up your calendar where you can schedule people to work on the job:

If you need to reschedule an event, the quickest way to do so is to click the View in Calendar button beside it:

Once everyone's time is entered, you can click Mark Labour as completed if they have not done so themselves: