Getting Start and end Date of Running Project

This will allow for you to attain the duration in milliseconds:

//record start time
var start = new Date().getTime();

/*
    run scripts
*/

//record end time
var end = new Date().getTime();

//calculate the duration in milliseconds
var duration = (end - start);

//in seconds
var durationseconds = duration / 1000;

//so on and so forth

You can use TestComplete's built in methods to attain the date and time:

//Log the start time of the script
Log.Message("Script was started at: " + aqDateTime.Now());

/*
    run scripts
*/

//Log the stop time of the script
Log.Message("Script was stopped at: " + aqDateTime.Now());