In order for us to give you an estimate, we'll ask you to indicate the approximate length of the task when you make the booking.
This can be done by creating a task and filling in certain information, including the estimated duration of the task. More information about creating your order can be found here.
Task duration may change if the pro informs you that they will need more time to complete the job. In that case, you'll be able to modify the estimated length of the task in accordance with your new agreement.
Also, keep in mind that the actual length of the job may differ from the estimated one, and the time reflected in your invoice will correspond to that of the actual time spent on the task. The final duration will always be the one submitted by the pro once they have completed the task.