To make certain fields completely invisible by the end users of OnTime, you will need to make this change in the custom field templates which will disable the view for all users. You can enable "Advanced Security Settings" under Tools > Manage Security Roles window which will not make the fields invisible but rather non editable. When the desired user security role is selected in the manage security roles window, click on the "Advanced" icon which is located on the toolbar. Enabling field-level security will allow you mark certain field as non editable by the user who is assigned to this particular security role in the OnTime application.