"Ab zwei Uhr ist das Restaurant nicht mehr offen."
This sentence seems to have stimulated a very fruitful discussion!
For one, it explains the German adverb "ab" when used with time. "Ab zwei Uhr .." includes all times that start at 2 o'clock and then follow 2 o'clock. It may help to draw a clock and draw examples of adverbs and times in it. For instance "Vor zwei Uhr" = before 2 o'clock, "um drei Uhr" = at 3 o'clock.
Then, "nicht mehr offen" expresses the fact that the restaurant is "not open [anymore/any longer]". Please translate as closely and naturally as possible in translate challenges. We do not offer dialogue challenges at Duolingo yet, but most likely a question such as "Is the restaurant still open at 2.30pm?" could have prompted such a response.
Yep it's wrong, remember that "the" and "that" are common translations for "das" and "this" is quite rare; also watch where you put "isn't" in the English sentence, your wording sounds like a question asking whether or not the restaurant is open.
This is the closest correct wording: "From two o'clock the restaurant isn't open any more."
also "ab" means "from" not "at" so your initial translation should have been "The restaurant is closed from 2"
and finally you don't need to 'meet' a word order, duolingo should accept any translation that means the same thing (if it doesn't use the "report a problem button" to suggest your sentence)