I'm not sure if there is an easy way to do this with a macro or journal. Perhaps someone else could chime in about that.
A simple but not very elegant method is to use a post called "program length and time" that should be a default post in your post directory. You can post individual operations or a group and display the results by checking "list output" at the bottom of the post processing dialog. In the display window you can then print the result or save it as a text file. Just so you know, this post behaves as a non-turbo mode post so large programs will take a bit of time to process.
Using custom commands you can also output time info in a nc file as well as in shop docs. I haven't done any fancy custom commands so I just output the time at the end of the nc file with a basic custom command someone gave to me. I was thinking about customizing my shop docs more but when nx8 came out with a different format I decided to hold off and I have not yet had a chance to customize the new nx8 docs. The new doc format can be customized without Tcl-Tk knowledge as well as having the ability to output individual program groups whereas the old advanced html docs cannot.