I think 我妹妹十一点上学 should be accepted since you usually don't need to include 的 when referring to people you are close to.
I think you are right
You thought right, I reporte it right now because it's still not fixed
Agree with this comment
You don't need 的 for family members. Please fix all of your sentences.
Still not fixed. :(
I reported the mistake. We don't need "de" for familiars.
I keep reporting this too.
Agree with this one,still typo
To my understanding, isn't there usually a phrase to articulate whether the 11 is a.m. or p.m.? Are there circumstances where, like here, it is omitted?