The 351 prefix is allocated to Portugal, which has three timezones [1]:
Europe/Lisbon, Atlantic/Azores and Atlantic/Madeira
Continental Portugal uses Europe/Lisbon for the whole territory, whereas the
prefix 351291 belongs to Funchal (referenced in the geocoding tables), which is
on the Madeira island and thus uses Atlantic/Madeira.
[1]: https://www.iana.org/time-zones
3497|Europe/Madrid
3498|Europe/Madrid
350|Europe/Gibraltar
-351|Atlantic/Azores&Atlantic/Canary
-35121|Atlantic/Canary
-35122|Atlantic/Canary
-35123|Atlantic/Canary
-35124|Atlantic/Canary
-35125|Atlantic/Canary
-35126|Atlantic/Canary
-35127|Atlantic/Canary
-35128|Atlantic/Canary
-351291|Atlantic/Canary
+351|Europe/Lisbon&Atlantic/Azores&Atlantic/Madeira
+35121|Europe/Lisbon
+35122|Europe/Lisbon
+35123|Europe/Lisbon
+35124|Europe/Lisbon
+35125|Europe/Lisbon
+35126|Europe/Lisbon
+35127|Europe/Lisbon
+35128|Europe/Lisbon
+351291|Atlantic/Madeira
351292|Atlantic/Azores
351295|Atlantic/Azores
351296|Atlantic/Azores