How Fix this Average calcu.?

[see PROB tab; in upload]
9.25 is obviously not the avg., of numbers [pink hilite].
Where’s my err?

Thanks! a18NTseg2 - Copy.ods

Well - had you tried to search the forum for questions rergarding the time formatting and operations with times?

One.

Two.

Three.

Four.

Five.

Unfortunately, theose who asked those questions didn’t pay attention to guidelines for asking, but still got relevant information, that you may consult now.