300 uSv/h is a helluva dose rate Marc. 24 hours and you have a (certain) lethal dose, 15 hours and you're going to be very ill indeed (skin sloughing, hair falling out, vomitting etc). I assume they're running a rota. Self sacrifice although noble is actually a pointless excercise as your hosts discovered during the war. I would think that 1-2 hours on then off for a few weeks. I'm not sure of the fractionation details but the health phycisists, med phycisists and rad-ocologists would have it dialled.
I think I mentioned I have worked on devices that were in that range but for 5 minutes and then no exposure for a month. If you're interested the device was a berylium target. We started with two but because of sanctions reverse-engineered another two to reduce our exposure.