Is the Umm Al-Qura calendar for prayer times suitable for Muslims in Italy, or is the North American calendar more suitable, and what is the correct method for calculating prayer times in Italy?

The fundamental principle for knowing the beginning of a prayer's time is the observable cosmic signs that the Lawgiver made indications for the entry of prayer times. One should not rely entirely on the temporal calendar for prayers, because the calendar is a matter of ijtihad (independent reasoning), and astronomical calendars can be used for approximation. It is not permissible to rely on the Umm al-Qura calendar or the North American calendar due to a significant time difference. One must rely on the cosmic signs, or seek a reliable calendar from trustworthy scholars. If it becomes clear that the prayers were not performed at their designated time, then they must be re-offered according to the majority of scholars.