Until then, against me first and last (8)
I believe the answer is:
meantime
'until then against' is the definition.
I can't judge whether this definition defines the answer.
'me first and last' is the wordplay.
'first' becomes 'a' (first letter of the alphabet).
'and' becomes 'n' (common abbreviation for 'and').
'last' becomes 'time' (I can't explain this - if you can you should give a lot more credence to this answer).
'me'+'a'+'n'+'time'='MEANTIME'
Can you help me to learn more?
(Other definitions for meantime that I've seen before include "interval" , "interim?" , "For the moment" , "Intervening period" .)