I regularly make flatbread, using a bread machine to make the dough, then rolling out flat and throwing onto a hot griddle pan.  The breads start to bubble within a few seconds and when cooked (1 - 2 mins) are beautifully soft and puffy.

However, I recently cooked some for a dinner party, and to save time and effort, I rolled out the breads a couple of hours ahead of time, instead of rolling them immediately prior to cooking as I do normally.  I stacked them with sheets of grease proof paper between each bread and kept them at room temperature until I needed to cook them.

When I put them in the pan to cook, they hardly bubbled or puffed up at all and instead just lay there in the pan.  When cooked, they were considerably denser and harder than normal and nothing like the delicious, light breads I normally get.

Can anyone shed any light on why this might have happened?  Is it because they had been sitting out for a couple of hours before cooking?  I wouldn't have expected this to affect them but I'm wondering if it did.

If so, how could I prepare such breads for a dinner party in advance so that I don't have to roll them out at the last minute?

Many thanks, James