Thanks for your replies, JohnC and Alessandro71.
If it's not on all Samsung phones, it's hard to find out if my function is working correctly or not.
So it's not possible to compensate for the 5 minutes.
But today I found out, that my function is also reading the next calendar alarm. This, by the way, with the correct time.
I have a reminder in my calendar for tomorrow 9:30, but no alarm clock alarm set.
My function is returning 9:30 of tomorrow.
This is what also
Alessandro71's App SleepClock returns.
@Alessandro71: Is this also only on my phone, or general on all phones?
Is it possible to read only alarm clock alarms?