Translation:What time does this store open?
あけます is the transitive form of the verb, focusing on the fact that somebody is acting upon something to open it. So for example: ドアをあけます - I open the door.
あきます is the intransitive form of the verb, focusing on the act of opening, or something opening itself. So for example: ドアはあきます - The door opens. このみせは何時にあきますか - When does this store open?
Is this how a native speaker would ask when the shop opens? I feel like I've seen another way of asking this that uses "nanji kara" instead.
Why "What hour does this store open?" is wrong? It is just "ji", not "jikan", no time period.
In American English when we want to know at what hour something opens we say "what time".
"What time is this store open" is not accepted by DL. Does anyone know the reason?
The verb in this sentence is "open". You can't use a simple present tense verb with "is". "What time does this store open?"
Edit: Actually now that I re-read this, I see that you could say "what time is this store open", meaning what are its hours. That's grammatically possible, but is not the meaning of the Japanese sentence, which is asking what time the store first opens for business.
Duolingo is quite inconsistency. In this lesson, one answer is "is open", another is "does open". I think the correct one should be "is opened". i.e. What time is this store opened?
They should also be more consistent or explanatory in theire use of お店 and 店 or store. Adding o in front of 店 makes it more formal. If they want to drop the formality then the formal option should also be listed under the word definition. Not to mention tge kanji as well. When it comes to languages one must go all in in providing explanations. It can make the difference between a poor learning experience and a good one.