const int c_LinkerTimestampOffset = 8;

int secondsSince1970 = System.BitConverter.ToInt32(b, i + c_LinkerTimestampOffset);

typedef struct _IMAGE_FILE_HEADER {
    WORD  Machine;
    WORD  NumberOfSections;
    DWORD TimeDateStamp;
    DWORD PointerToSymbolTable;
    DWORD NumberOfSymbols;
    WORD  SizeOfOptionalHeader;
    WORD  Characteristics;
} IMAGE_FILE_HEADER, *PIMAGE_FILE_HEADER;

IMAGE_FILE_HEADER header;
char* start = (char*)&header;
char* field = (char*)(&header.TimeDateStamp);
int diff = field - start;

typedef struct _IMAGE_NT_HEADERS {
    DWORD Signature; //<- we need to skip this
    IMAGE_FILE_HEADER FileHeader;
    IMAGE_OPTIONAL_HEADER32 OptionalHeader;
} IMAGE_NT_HEADERS32, *PIMAGE_NT_HEADERS32;

int secondsSince1970 = System.BitConverter.ToInt32(b, i + c_LinkerTimestampOffset);

public class IMAGE_FILE_HEADER
{
     public UInt16 Machine;
     public UInt16 NumberOfSections;
     public UInt32 TimeDateStamp;
     public UInt32 PointerToSymbolTable;
     public UInt32 NumberOfSymbols;
     public UInt16 SizeOfOptionalHeader;
     public UInt16 Characteristics;
}