A family of Microsoft word processing software products for creating web, email, and print documents.
When you go into Insert> Date and Time... scroll to the bottom of the list & select one of the last 2 formats (depending on whether you want to include seconds in addition to hours & minutes). If you do not want the time to update automatically every time the document is opened be sure that the box is not checked.
If you use the Insert> Field method suggested by trip_to_tokyo the field will automatically update unless you take an extra step to UnLink the field. IOW, using this method is the same as checking the box in the Date and Time dialog whereas using the dialog inserts the Date/Time as static text if the box isn't checked.