The shifts, they are a-changin’ at the Tustin Police Department. Every six months, the department goes through a shift change. Personnel work hours turn from days to nights or nights to days, all in the name of keeping the Tustin streets, homes and businesses safe 24/7. This transition affects more than half the department, and decisions are determined by seniority, said Sgt. Natalie Nguyen, a 16-year department veteran who transitioned from nights to days. “It’s a relatively easy transition,” Nguyen said. This change also brings the officers into a different set of typical calls for service. For example, daytime calls…