Obtener sobre.es decir, lapsos de tiempo superpuestos

Prueba este también. Lo probé lo mejor que pude, creo que cubre todas las posibilidades, incluida la fusión de intervalos adyacentes (10:15 a 10:30 y 10:30 a 10:40 se combinan en un solo intervalo, 10:15 a 10:40 ). También debería ser bastante rápido, no consume mucho.

with m as
        (
         select ip_address, start_time,
                   max(stop_time) over (partition by ip_address order by start_time 
                             rows between unbounded preceding and 1 preceding) as m_time
         from ip_sessions
         union all
         select ip_address, NULL, max(stop_time) from ip_sessions group by ip_address
        ),
     n as
        (
         select ip_address, start_time, m_time 
         from m 
         where start_time > m_time or start_time is null or m_time is null
        ),
     f as
        (
         select ip_address, start_time,
            lead(m_time) over (partition by ip_address order by start_time) as stop_time
         from n
        )
select * from f where start_time is not null
/