How do I calculate how long a furnace has to work to compensate a given temp drop?
The vast majority of home heating thermostats do not have a user configurable "temperature drop before the thermostat calls for heat" or hysteresis. It is what it is, and it's usually small.

To calculate the temperature rise, you need to know many things, some of which vary. In particular, the insulation (resistance to heat flow) of the structure, and the external temperature. The thermal mass of the building and contents also come into play, as does air leakage and/or deliberate ventilation; air leakage will generally vary with wind speed and direction outside the house.

The net effect in practice is that the furnace works longer as it gets colder (and/or windier) outside. If you monitor how much the furnace (burner) runs in an hour, you can infer the rate of heat delivery required to maintain temperature for that hour (If it runs for 30 minutes and is a 60,000 BTU/Hr furnace, the house needed 30,000 BTUs for that hour.) An ideally sized furnace will run 100% of the time on the coldest day you get (and maintain temperature in the house while doing that.)