How to get the elapsed time of Microsoft TTS speech?

I now use following function to realize a TTS service.

int tts(LPCWSTR text){
    ::CoInitialize(NULL);         
    CLSID CLSID_SpVoice;
    CLSIDFromProgID(_T("SAPI.SpVoice"), &CLSID_SpVoice);
    ISpVoice *pSpVoice = NULL;
    IEnumSpObjectTokens *pSpEnumTokens = NULL;

    if (FAILED(CoCreateInstance(CLSID_SpVoice, NULL, CLSCTX_INPROC_SERVER, IID_ISpVoice, (void**)&pSpVoice))){
        return -1;
    }

    if (SUCCEEDED(SpEnumTokens(SPCAT_VOICES, NULL, NULL, &pSpEnumTokens))){
        ISpObjectToken *pSpToken = NULL;
        SpFindBestToken(SPCAT_VOICES, L"Gender=Male", L"Name=Microsoft Simplified Chinese", &pSpToken);
        pSpVoice->SetVoice(pSpToken);
        pSpVoice->Speak(text, SPF_DEFAULT, NULL);
        pSpEnumTokens->Release();        
    }

    pSpVoice->Release();
    ::CoUninitialize();
    return 0;
}

Is it possible for me to get the elapsed time of each character being spoken? Or is it constant (if the speech rate is set)? The purpose is that I want to show some facial animations to match the speech...