How can I track time from the command-line?

This answer suggests to use

time cat

and use Ctrl-D to see the time.

You can also use

time read

and use Enter key

Also check this answer on the same question

How about:

stopwatch() { 
    local start=$SECONDS
    read -p "Hit Enter..."
    echo $((SECONDS-start)) seconds elapsed
}

In action:

$ stopwatch 
Hit Enter...
14 seconds elapsed

Simple way of doing it is to take start time, and once you stop the script - take stop time. Finally, print the time difference. This can easily be done with Python:

python -c $'import time;start=time.time();\ntry:\n\twhile True: time.sleep(0.25)\nexcept: print(time.time()-start)'

Or long version for readability:

import time
start=time.time();
try:
    while True: time.sleep(0.25)
except: 
    print(time.time()-start)

Stopping is done with Ctrl+C