English term (edited): no shipment dates shall fall within the meaning of

"No obstante las fechas de envío se considerará término esencial". Try also: "No obstante las fechas de envío no se reputarán término esencial" or "caerán dentro de la definición de "término esencial"

This means that the parties will use their best efforts to comply with any shipment dates. However, in the event of non-compliance no liability would arise for any of the parties because it shipment dates are not essential (or "of the essence"). The equivalent in Spanish law is término esencial u obligaciones sometidas a término esencial (i.e. if you fail to meet the particular date then you are liable).

Best of luck

Alex

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Note added at 11 mins (2006-06-06 19:05:08 GMT)
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Sorry, the first sentence should read "No obstante las fechas de envío NO se considerarán término esencial"