fixed with header guard main

_main.cpp

...
#ifndef TIME_H
#define TIME_H  
// replaced from first #include "time.h"
struct Time {
    int hour;
    int minute;
};
...
#endif
...

// replaced from #include "util.h" which also include "time.h"
#ifndef TIME_H
#define TIME_H  
struct Time {
    int hour;
    int minute;
};
...
#endif

...  
  
int main(){
...
}