For items that are in an Exchange calendar the correct date is selected in the Calendar app, but the appointment is not selected. For items that are in the iOS calendar the item is selected in the Calendar.app but not opened.
That makes sense, Exchange calendar items don’t have a stable identifier that we can use to pinpoint the right event therefore it only goes to the day. For iCloud events they can be selected. In general with what APIs Apple offers we can’t “open” the calendar items, we can only select them.
And since this uses AppleScript, which is not available on iOS, on the latter we can only open the calendar on the right day alas.