By default, the Start Time on the Weekly and Multi-line data-entry screens is set to 12.00 a.m. But this can be configured to be whatever makes sense for your organization. And the setting is sensitive to your user's dektop time. For example, if you set it to, say, 08:30, your users will see that as the default starting time whether they are on the East Coast in the US or in Europe. So it works to speed up data-entry no matter where you are.
Currently, the Config screen in the TimeTracker does not support changing the default time. Please contact your Salesforce Administrator if you want to change the default time on the Weekly and/or the Multi-line tabs. They will contact PK4 Technologies to make the change.