char temp[100];
int i = 0;
clock_t start, end;
double difftime = 0;

while(1) {
    memset(temp,0x00,sizeof(temp));
    ComPort1->Read(temp,100);
    for(i = 0;  i < 100; i++) {
        if(temp[i] == '1') break;
    }
    if(temp[i] == '1') break;
}
start = clock();
while(1) {
    memset(temp,0x00,sizeof(temp));
    ComPort1->Read(temp,100);
    for(i = 0;  i < 100; i++) {
        if(temp[i] == '0') break;
    }
    if(temp[i] == '0') break;
}
end = clock();

difftime = (end - start) / CLK_TCK;
ShowMessage(difftime);

이정도면 되겠네요