SELECT distinct on (st.gid) sv.timing, st.gid, st.area
FROM servers sv
INNER JOIN sites st
ON (st_distance(sv.geom, st.geom)<8.5) where
        sv.workmode = 1 AND sv.timing >= timestamp '2018-02-02 00:00:00'
        and sv.timing <= timestamp '2018-02-02 23:59:59';

SELECT distinct on (st.gid) sv.timing, st.gid, st.area
    FROM servers sv
    INNER JOIN sites st
    ON (st_distance(sv.geom, st.geom)<8.5) where
            sv.workmode = 1;