Hey Tom, Salvo:
When you've swam with tempo long enough you know what your tempo range is both lower end and higher end (faster tempo) without a TT beeping next to your ear. I rarely swim an entire session on tempo, maybe 1/3 max, and mostly to reset my "inner tempo" or swim at tempos both above and below my range. Whether tempo is 1.05, 1.02, 1.0, .98, .95 - I know each one so well that I can hit those tempos at will and use each depending on distance and (in open water) changing conditions.
Challenge yourself on what your tempo range is and if you can hit tempos in that range at will. Test with turning tempo on and, counting strokes, pressure, and feeling.