How to adjust baking time if I adjust the quantities in the recipe? This video gives the following bread recipe:

1 kg flour
600 ml water
15 g yeast
18 g salt


After doing all the preliminary stuff you'd expect, you shape the dough into a ball and bake it in a Dutch oven at 250 C / 480 F for 30 mins, then lower the heat to 230 C / 430 F for another 30 mins.

The bread it produces is delicious, but that's a huge loaf of bread! Which leads to this question: if I halve all the quantities, do I also halve the baking time?
You would not half the baking time, but it might take slightly less time.  The best way to determine if it is done will be to measure the internal temperature.  Most bread is done when the internal temperature hits 190F (88C).