Bread proofing times fridge versus room temp
Basic room temperature breads don't prove in 6 or 12 hours, 30 minutes to 2 hours is more typical. The overall process from start to finish including baking may be 6 hours. Sourdough breads and enriched doughs like brioche and challah can take much longer to prove at room temperature. 

As for calculations no, there's no straightforward time conversion between room temperature and refrigerator proving because there are too many factors like actual room temperature and yeast potency which vary how long the bread will take to prove in other location. In home baking you prove to result, not to time, i.e. you prove until bread has doubled or tripled in size however long it takes. 

Refrigerator proving really does slow it down by a very large degree, I don't have a figure for it but what I will say is that if you made a dough in the morning then put it in the fridge for 10 hours it still may not be fully risen. This isn't a bad thing, it means you have a lot of flexibility. I often make pizza base the night before then leave it in the fridge for an entire day before using it with excellent results (that won't work for all types of bread as it may be too much proving). 

What that means for you is that you can be strategic with it; make the dough in the morning and then put it in the fridge to prove, when you come home if it isn't fully risen it's not a problem as you just take it out of the fridge and let it warm up on the counter until it has. Or you can make the dough in an evening, rise it overnight and bake it in the morning.