You should definitely reconfirm if you arrive after 18H00 local time, or if you intend to arrive earlier than the usual check-in time.

In general, it certainly does not do any harm to send a confirming e-mail, thanking them for their previous confirmation, citing the booking number and telling them you look forward to staying in their superb establishment. It is probably not required, but if done in a friendly way it will just reassure both sides.

Enjoy your trip to Spain!