The beat frquency is which in your example is equal to 5 Hz. So the frequency of the 'envelope' is 5 Hz and therefore the period is 1/5 sec. The periods of your two since waves are 1/440 and 1/445 sec.

So care is needed in choosing the window on your calculator ......

It might be easier, for graphing purposes, to use two frequencies that are closer to each other. Perhaps 440 Hz and 441 Hz .......