This is controlled agency-wide by a setting in the Settings Module > Setup Tab > Time Entry section. The setting is titled "Time(New) after save clear units/hours". When this setting is set to "No" the start time, end time, units, and hours will remain after saving the first service line. If "autopopulate hours/units" is enabled, hours will need to be re-entered on subsequent service lines however, this is the same functionality as Appointment Module.
