select client, status, min(time) as starttime,
       lead(min(time)) over (partition by client order by min(time)) as endtime
from  (select t.*,
              row_number() over (partition by client order by time) as seqnum,
              row_number() over (partition by client, status order by time) as seqnum_s
       from t
      ) t
group by (seqnum - seqnum_s), status, client;