Oh, it also states this at the Zoom website in the FAQ on the G5
Quote from G5 FAQ:
Is it possible to use a foot switch to tap the tempo used for delay times and modulation rates?
This is not possible using the foot switches on the G5. If you want to tap the tempo for delay times and modulation rates while playing guitar, you will need an FS01 foot switch (sold separately).
Also, please follow the procedures below to tap the tempo with an FS01 foot switch.
1) Select "TAP TEMPO" from the [CTRL SW] setting in the TOTAL menu.
2) Set the TIME/RATE parameter of the desired effect to a note symbol(♪).