Steven L. wrote:
I have to replace some dirty and moldy grout between the tiles above
the bathtub. But the grout I saw sold at the hardware store said
that it has to stay dry for 36 hours. That would be impossible,
unless I moved to a hotel for two days. I take two showers a day,
and that's the only bathroom I have in my home.

Can you recommend some really fast-drying or quick-drying grout
compound? It would just be for this small repair--maybe two square
feet of tile that needs to be regrouted.

Just tape plastic over the area.