When the dough has risen nearly double, turn on the oven and set it to 180 degrees centigrade

Once the oven is at that temperature, put the bread in.

I bake large, family-sized sourdough loaves that take around an hour to cook, and usually make a moist dough. Obviously a smaller loaf or a more dry dough will bake more rapidly - once the loaf is a medium brown, the chances are that it will be cooked. Factors such as the power of your oven will influence times, obviously.

You should then (using oven-gloves, please) remove the loaf from the oven and leave it to stand, out of the baking tin on a cooling rack for at least half an hour. Ideally leave it until cold.

One last comment - you will probably find that the yeast will "mature", becoming more effective as time goes on as it adapts to your choice of flour. In fact it is possible that your first loaf will be a good doorstopper !

Don't be discouraged if this is your initial result - there should be a steep improvement thereafter and around the third or forth loaf you will have a stable, effective sourdough yeast culture for as long as you wish - even to pass on to your children.