Hello and thanks for trusting me to help you today. I am a licensed diagnostic and repair technician, I look forward to working with you.This is not a common problem as far as I know, it's not something I have come across my self. The entire heating system is behind the dashboard and it is a big job unfortunately, the heater system is compressed in very tight so access is very poor and it is possible that ultimately the dashboard will need to come out. Before going down this route I would be inclined to ask them to remove the blower fan which will give some access to the duct work just to see if it is accessible. Of course it depends entirely on where the object is but I would give it a very good go at getting my hands in there first. Most garages now carry an endoscope which allows a small camera to be inserted on a flexi head which might locate the object, with the help of this they might be able to remove it so I would ask if they have one and if not take it to a garage that has one.With any luck the object can be removed, if not then unfortunately the dash board and heater ducts will need to be removed to gain access, although I think 8 hours is worst case i would expect 4-6 hours to be more realistic.
I hope this answers your question, if you need further assistance or would like more information please feel free to reply. Thanks, Ross.