Use
In the Cell Information dialog box, you can enter a short text for each record you create in the time sheet.

You have documented the following situations in a short text.
Short Text as the Long Text Header
The short text can also be used as the header of any
long text you enter for the record.Prerequisites
Your Customizing settings must determine that the Short text field is shown.
Procedure
The short text is displayed in the corresponding field in the Cell Information dialog box.
The data entry view for the time sheet reappears.