A learner given a brief time noted fort (5)
I believe the answer is:
alamo
'noted fort' is the definition.
(as in the Battle of the Alamo)
'a learner given a brief time' is the wordplay.
'learner' becomes 'l' (as in a learner driver with L-plates on their car).
'given' is a charade indicator (letters next to each other).
'brief time' becomes 'mo' (short for moment).
'a'+'l'+'a'+'mo'='ALAMO'
(Other definitions for alamo that I've seen before include "Famous Texan fortress" , "Texas mission taken by Mexican forces in 1836" , "Famous Texan mission" , "The --, Texan mission besieged in 1836" , "Famous battle in Texas launched by the Mexican army" .)