Though time can be displayed in the preview monitor, I don;'t think there is any way to include it in an export.
I'd suggest filming this display (full screen, no other image, text color of your choice) for the required time and then adding it as a new track using black chroma key and cropping to show just minutes and seconds. As MEP can't screen record itself you'd need another program to do this or perhaps just film it with a camera.
Maybe an alternative: Some time ago I wrote a little BASIC program to generate HR:MIN:SEC:FRAME numbers as a series of .BMP images which could be imported to produce a count down video. I'll see if I can find it if you're interested.
As a remark to Carl's answer: Start the MEP 2 times. (MEP warns you about problems, but continue.) Now you can record screen activity in MEP with the same program. I have done so many times.