In the movie Edge of Tomorrow, Tom Cruise recovers a particular item from the General's office.
is a prototype tracker Carter built that will allow Cage to discover the Omega's true location. After several failed loops they obtain the device and get it out of the General's office. During the course of recovering this tracker Cage and Vrataski are injured as they flee and an unconscious Cage is given a blood transfusion, losing the ability to reset.
Vrataski knows the tracker simply needs be activated and driven into Cage's leg to find the Omega, why did they have to leave the General's office and risk losing the ability to reset? i.e. why didn't they simply activate the device in the General's office, jam it into Cage's leg, learn the Omega's location and have Vrataski shoot Cage to reset the loop.
This approach would have had the benefit of being able to use the full loop time.
Also, because the ministry
did not believe Carter's explanation about the Alphas and Omega, it seems unlikely that Cage and Vrataski would have any reason to believe the tracker would be "jammed" or otherwise not function within the Ministry. Also, they could have easily used the General as a hostage to buy enough time to jab Cage, learn the location and kill him to reset the loop.