Perhaps someone is wondering about the answers later on:
1. The tape can remain as you don't grout the bottom row anyway, instead silicone is applied there. However, expect that it's a bit tricky to remove the tape.
2. It likely depends on the adhesive, but according to the manufacturer, I could have grouted the next day considering the current conditions.
3. No problems grouting, press the grout in with the trowel and then pull diagonally to clean up. Use a soft grout float!