Is it said, "We have entered upon morning, and the dominion has entered upon morning belonging to Allah" at noon, and what is said at Asr? And is the plural of "my parents" in supplication "our parents" when supplicating for a group?

The morning and evening remembrances (adhkar) have specific times. The morning time begins from midnight and ends at noon (zawāl), while the evening time begins from noon (zawāl) and ends at midnight.

As for the word "al-walidayn" (parents), "walid" (parent) is pluralized as a sound masculine plural "walidūn" because it is an adjective for a rational male, devoid of the feminine ta' (تاء التأنيث). Therefore, when it is appended to the plural pronoun, it is said: "Allāhumma ighfir liwālidīnā" (O Allah, forgive our parents), with a kasra on the dāl, and it is in the genitive case with a yā' because it is a sound masculine plural.