Clue: Final flag hoisted above ship's stern, done in desperation at the eleventh hour (4-4)
Answer: LAST GASP
Explanation: Definition: done in desperation at the eleventh hour
 LAST(final/the one coming at the end) + **reversal of**(… hoisted, in down clue) SAG(to flag/to weaken) **placed above**(above, in a down clue) **last letter of**(…'s stern) "ship".