With Type Pilot, you can insert the current date / time.
Create a new phrase, where you are going to use current time (date).
In the Edit Phrase window, go to the Insert | Time menu item and select a desired time format string. You can also click Custom… item to define your own format.
The following string is inserted.
Complete your phrase and assign a keyword (for example, tm) to it.
Now, if you enter this keyword anywhere, you get the current time.
You may wish to insert current date and time into your letter signature, as in the following example: