Entering time will not directly impact duration or work. Time typically represents the actual effort on a task, while work is the estimated effort. Duration is the number of days allotted in which to do that work. Reporting time can impact the % completion depending on how your system is configured. As an example, let's say a task has 4 hours of work and you report 2 hours of time. By default the % completion would be 50% if you have "Actual effort reported from timesheet" checked on for that task. You can also over-ride this % if you know that a task is going to be completed early or will require more hours than originally forecasted in the work field.