This works on Meet Manager 4 (yes, I know it's an old version).
Go to Setup->Report Preferences. On the Report Formats tab, check the box next to "Display NT for results under 5 seconds." Click OK.
Go to the run menu, find your event. Enter .01 for first, .02 for second, .03 for third, etc. Score the event. The report will dispaly NT for everybody with a mark less than five seconds, but will score it properly.
I checked and you can also use the JD button if you only missed a couple of times rather than an entire heat. Say you got 1st, 2nd, 4th, 5th, and 6th. But the timer who was supposed to hit the button for 3rd wasn't paying attention. Put in the correct times for the 5 you got. Put in something below 5 seconds for the third place team. Then use the JD button to assign the places as needed. 3rd will be given the correct points, but will have an NT.