Printing time values along with pose

I’m an absolute newbie and I got hold of someone’s simple program to navigate a robot by setting a goal position and including random obstacles. The python script uses ROS move_base and navigation packages, subscribes to nav_msgs and prints out pose and twist outputs to the terminal/a text file. Everything works fine but I’m not able to figure out the time values for each pose/twist output. How can I get the script to output time; or is it an output frequency parameter set in any of the yaml files. I tried searching and I could not figure out.