Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: Time
SUNEXPRESSIONTAG_DATETIMEParameter: Current Time
SUNEXPRESSIONTAG_TIME_NOWParameter: Today
SUNEXPRESSIONTAG_DATE_TODAYParameter: Animate Date
SUNEXPRESSIONTAG_INTERPOLATE_DATEParameter: Animate Time
SUNEXPRESSIONTAG_INTERPOLATE_TIMEParameter: City
SUNEXPRESSIONTAG_POS_CITY_COMBOParameter: Latitude
SUNEXPRESSIONTAG_LATITUDEParameter: Longitude
SUNEXPRESSIONTAG_LONGITUDEParameter: Time Zone
SUNEXPRESSIONTAG_POS_TIMEZONEParameter: Daylight Saving
SUNEXPRESSIONTAG_POS_DST_SETTINGSParameter: Time Zone Diff.
SUNEXPRESSIONTAG_POS_TIME_ZONEParameter: DS Time Zone
SUNEXPRESSIONTAG_POS_DST_TIME_ZONEParameter: Distance
SUNEXPRESSIONTAG_DISTANCEParameter: Set Light Color
SUNEXPRESSIONTAG_SETLIGHTCOLOR