 The above comments apply here also.However, since the Amidah is only rabbinically required (unlike the Shema which is Scriptually mandated) it is common to rely on the later time, thus only a few calendars publish the earlier time.Midday (חֲצוֹת הַיּוֹם, "Chatzot Hayom" or just "Chatzot") means the midpoint between sunrise and sunset, or equivalently between daybreak and sundown.