Group (count) values every hour

Hi there, I have a rain sensor now in place that gives me a line of data on every about 2ml in a 5*8 cm funnel on every “flip and flop”. Now I try to vsualize it, and I want to summarize hours. I have the feeling that thes query result (see pic) is correct, because it matches the rain going down, but why is that bar “smaller” than 1 hour?:

data lines look like:

> select time,Kontakt from P41 where Sensor='Regen' AND Kontakt =     true
name: P41
time                Kontakt
----                -------
1606818655619416399 true
1606818669116364827 true
1606818759524299576 true
1606818825207480715 true
1606818826300389372 true
1606818827487356476 true