Green’s Dictionary of Slang

(S.Afr.) used as a greeting in the S. Afr. army by national servicemen who have 40 or fewer days to serve; also the period of service itself.

1971		on Radio S. Afr. 31 Dec. n.p.: The only reason we could bear to cross them [i.e. weekends] off at all was that any crossing off of days brought us nearer and nearer to the end of yet another term like the army and their ‘min dae’ [DSAE].
1977		G. Hugo in Quarry 77 95: ‘Don’t tell anyone, hey, but you’re going to be permanently discharged.’ His thick face breaks into a grin. ‘Min dae, hey.’ [DSAE].
1983		W. Steenkamp Borderstrike! Another universal phrase was ‘min dae’, literally ‘few days’, meaning a serviceman’s tour of duty was almost complete.