Boost has the DateTime library, but it doesn't allow setting the time.
What you have here are absurd conflicting requirements. I still think that changing std_types.h is the correct thing to do. It sounds like this is some course assignment, though, and teachers can be stubborn.
You could also declare just the API functions you need. The undecorated prototypes of GetSystemTime and SetSystemTime are:
Code:
extern "C"
{
struct SYSTEMTIME
{
unsigned short wYear;
unsigned short wMonth;
unsigned short wDayOfWeek;
unsigned short wDay;
unsigned short wHour;
unsigned short wMinute;
unsigned short wSecond;
unsigned short wMilliseconds;
};
void __stdcall GetSystemTime(SYSTEMTIME *pSystemTime);
int __stdcall SetSystemTime(const SYSTEMTIME *pSystemTime);
}