select
extract(hour from t1.dt) as hour,
t1.dt as t1, t0.dt as t0,
round(((t0.ambtemp + t1.ambtemp) / 2)::numeric, 2) as average
from
n25 t0
inner join
n25 t1 on
date_trunc('minute', t0.dt + interval '1 hour - 2 minutes')
= date_trunc('minute', t1.dt)
where extract(minute from t1.dt) = 41
order by t1.dt