How long will 10 gallons of diesel fuel last in my oil furnace?

There is really very little chance of anyone being able to answer this question accurately without knowing the type of the furnace, outside temperature, wind chills, house insulation values, your desired indoors temperature etc, etc. There are just way too many factors. Consumption rates of 1-2 Gallons per hour, when the furnace is on are within the norm, but it is hard to say how long the furnace has to stay on. In the US North East right now (late Feb 2015) I cannot imagine it will last you more than 2 days. But you will have to adjust to your own conditions, of course.

Bout 48-72 hrs. 5 gallons lasts me less than two days.