Does proofing time depend on the quantity of dough? One recipe, for example, specifies the dough should be left to rise for 4 hours. If I make halt the amount of dough, will the proofing time change? 
I'm not providing the recipe because I will be trying and experimenting with many in the next few days.
No.

The proofing time of a dough is a function of the ratio of yeast and available water, and the temperature of the dough. Notice these are ratios. If you doubled a recipe but didn't double the yeast with it the dough would rise much more slowly.

The quantity of dough will only play a role in rise time if the dough is a significantly different temperature than the surrounding environment. In this case the dough in the center will rise at a different rate than the dough on the outside.