I think the answer to your question lies not in ticks of the clock but in the heart and soul of your lyric. You have to decide for yourself if you have written too little, or too much. Besides, there are so many variables that it would be madness to try to quantify it, IMO.

If you really believe that there is some mathmatical formula, then get out your stopwatch, queue up a bunch of songs you like, count the words and do the math. The results might be very interesting....or even instructive.