English to Spanish Bus/Financial Law: Contract(s)

For Milestone V to become due and payable in favour of the Developer, RTB (Ready to Build) shall be reached for the Project in the twenty-four (24) months after having obtained the IVA (the “Milestone V Longstop Date”).

A phrase that keeps nagging me for a possible translation would be: "Fecha límite para la finalización del Hito V"

What's not letting me move on is this:
The translation is too wordy and breaks one of translation's golden rules: concision
There are a couple of translations for this phrase:
-Fecha de Finalización del Hito
-Fecha de Fin del Hito
-Fecha límite del Hito
When looking into it, longstop means date which cannot be surpassed, and if I were to go by intended meaning, it gets hard to narrow the choice of words down to a few.

Any tips what would be the ideal, or best sounding translation?