The charges are applied in a fixed rate for every task. If the actual time consumed is shorter than the set duration, you will still be charged based on the latter.
If your task will take longer than expected, kindly send a message to the partner directly through the chat feature and inform him/her about this. The partner may also be the one to request for an extension should the initial time be insufficient for them to complete the task. You may then extend the job through the “Extend Job” feature which you can see upon clicking the three dots on the top right corner of the app, after selecting the specific job you wish to extend.