1  WITH t as (
  2  select to_date('26.11.2016 16:54:22','dd.mm.yyyy hh24:mi:ss') d from dual union all
  3  select to_date('26.11.2016 16:55:24','dd.mm.yyyy hh24:mi:ss') d from dual union all
  4  select to_date('26.11.2016 17:00:15','dd.mm.yyyy hh24:mi:ss') d from dual union all
  5  select to_date('26.11.2016 17:02:07','dd.mm.yyyy hh24:mi:ss') d from dual union all
  6  select to_date('26.11.2016 17:02:40','dd.mm.yyyy hh24:mi:ss') d from dual union all
  7  select to_date('26.11.2016 17:13:47','dd.mm.yyyy hh24:mi:ss') d from dual union all
  8  select to_date('26.11.2016 17:14:15','dd.mm.yyyy hh24:mi:ss') d from dual union all
  9  select to_date('26.11.2016 17:14:46','dd.mm.yyyy hh24:mi:ss') d from dual union all
 10  select to_date('27.11.2016 16:48:30','dd.mm.yyyy hh24:mi:ss') d from dual union all
 11  select to_date('27.11.2016 16:48:31','dd.mm.yyyy hh24:mi:ss') d from dual union all
 12  select to_date('27.11.2016 16:52:15','dd.mm.yyyy hh24:mi:ss') d from dual
 13  )
 14  ,tt as (select d,case when d-(lag(d,1,d) over (order by d) )<=1/24/6 then 0 else 1 end f from t)
 15  ,ttt as (select d,sum(f) over (order by d) gr from tt)
 16* select min(d) d_from,max(d) from ttt group by gr order by 1
SQL> /

D_FROM              MAX(D)
------------------- -------------------
26.11.2016 16:54:22 26.11.2016 17:02:40
26.11.2016 17:13:47 26.11.2016 17:14:46
27.11.2016 16:48:30 27.11.2016 16:52:15