Large number finally get short time on beach (8)
I believe the answer is:
thousand
'large number' is the definition.
(I've seen this before)
'finally get short time on beach' is the wordplay.
'finally' indicates one should take the final letters.
'short time on' becomes 'hou' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'beach' becomes 'sand'.
The last letter of 'get' is 't'.
't'+'hou'+'sand'='THOUSAND'
(Other definitions for thousand that I've seen before include "Cardinal" , "See 19 Across" , "in MCC, but missing double century" , "Large number" , "Ten hundreds" .)