Hi Ye Wan,
I am using the same BAPI and its working for the date the user confirms it.
You can find the code below.
"" GET DETAILS IN TABLE QPAC ""
st_SetUsg_BAPI-wa_UD_DATA-INSPLOT = st_Sel-INSPLOT.
st_SetUsg_BAPI-wa_UD_DATA-UD_SELECTED_SET = '03'.
st_SetUsg_BAPI-wa_UD_DATA-UD_CODE = 'A'.
st_SetUsg_BAPI-wa_UD_DATA-UD_CODE_GROUP = '03'.
st_SetUsg_BAPI-wa_UD_DATA-UD_PLANT = '0001'.
st_SetUsg_BAPI-wa_UD_DATA-UD_RECORDED_BY_USER = SY-UNAME.
st_SetUsg_BAPI-wa_UD_DATA-UD_RECORDED_ON_DATE = SY-DATUM.
st_SetUsg_BAPI-wa_UD_DATA-UD_RECORDED_AT_TIME = SY-TIMLO.
st_SetUsg_BAPI-wa_UD_DATA-UD_TEXT_LINE = 'Confirmation'.
st_SetUsg_BAPI-wa_UD_DATA-UD_FORCE_COMPLETION = 'X'.
st_SetUsg_BAPI-wa_UD_DATA-UD_STOCK_POSTING = 'X'.
st_SetUsg_BAPI-wa_LANGUAGE-LANGU = 'E'.
st_SetUsg_BAPI-wa_LANGUAGE-LANGU_ISO = 'EN'.
CALL FUNCTION 'BAPI_INSPLOT_SETUSAGEDECISION'
EXPORTING
NUMBER = st_Sel-INSPLOT
UD_DATA = st_SetUsg_BAPI-wa_UD_DATA
LANGUAGE = st_SetUsg_BAPI-wa_LANGUAGE
IMPORTING
UD_RETURN_DATA = st_SetUsg_BAPI-wa_UD_RETURN_DATA
STOCK_DATA = st_SetUsg_BAPI-wa_STOCK_DATA
RETURN = st_SetUsg_BAPI-wa_RETURN.
Hope it helps,
Regards,
Anirudh.