
Answer:
In some clock applications, for example, the clock App on a Samsung
phone, the next alarm has been registered to Android operating system
with 5 minutes earlier ( could be any number of minutes, at least, on
Samsung phone, it's 5 minutes ).
How to fix it:
Go
to menu Settings, section "Value Adjustment", switch on it, and set
value 5 in "Value Delta" editbox. See the snapshot at the right side.
Remark: This will fix the main entry time of the next alarm, but not fix the following snooze times (if there are)