Well, if you are doing the startup like instructed in the training mission, then, no, that line will not flash, it will not even display at that point.
Usually, once you are finished uploading the DTS data, you'll push the OSB for the CDU page on the right MFCD and the OSB for the TAD page on the left MFCD.
The first line of the CDU page reads Align plus a few numbers letters, the second line is at the start blank, then, after some time it will show INS NAV RDY and after that, when the eight line from the top shows T= 4.0 0.8, the INS NAV RDY will start to flash.
Now, for the display of the map it only matters that the line INS NAV RDY displays steadily, when it does you can press the OSB for Nav and the map will display on the TAD page on the left MFCD, however, I usually will wait until INS NAV RDY flashes, as otherwise the EAC will not turn on.
See also page 438 in the manual to see how the CDU display on the MFCD should look like before pressing NAV.