Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: Time
SUNEXPRESSIONTAG_DATETIME
Parameter: Current Time
SUNEXPRESSIONTAG_TIME_NOW
Parameter: Today
SUNEXPRESSIONTAG_DATE_TODAY
Parameter: Animate Date
SUNEXPRESSIONTAG_INTERPOLATE_DATE
Parameter: Animate Time
SUNEXPRESSIONTAG_INTERPOLATE_TIME
Parameter: City
SUNEXPRESSIONTAG_POS_CITY_COMBO
Parameter: Latitude
SUNEXPRESSIONTAG_LATITUDE
Parameter: Longitude
SUNEXPRESSIONTAG_LONGITUDE
Parameter: Time Zone
SUNEXPRESSIONTAG_POS_TIMEZONE
Parameter: Daylight Saving
SUNEXPRESSIONTAG_POS_DST_SETTINGS
Parameter: Time Zone Diff.
SUNEXPRESSIONTAG_POS_TIME_ZONE
Parameter: DS Time Zone
SUNEXPRESSIONTAG_POS_DST_TIME_ZONE
Parameter: Distance
SUNEXPRESSIONTAG_DISTANCE
Parameter: Set Light Color
SUNEXPRESSIONTAG_SETLIGHTCOLOR