Final answer:
The question about the amount of return time cut off by the loss of thrust cannot be answered without additional information; however, it is important to note that the pilots' actions resulted in a safe landing without power.
Step-by-step explanation:
The incident described involves the loss of thrust in a Boeing 767, which resulted in the aircraft losing all power and effectively becoming a glider. The specific reduction in return time due to this loss of thrust is not mentioned in the provided information, and would require additional data such as the distance remaining, the glide ratio of the aircraft, and prevailing wind conditions to calculate. In this unprecedented situation, Captain Robert Pearson and First Officer Maurice Quintal efficiently handled the emergency by deciding to land at the former Gimli air force base, converting a potentially catastrophic situation into a successful landing with no fatalities. The skillful actions taken drastically cut down the total time the aircraft would have been in the air without power.