-Every line is separated into 8 parts by colons

-Every part can include words,numbers,space etc.

I am trying to replace the space in the 6th part with a colon, thus separating the line again, making the total number of parts 9.

 1;30;68;Az LEMda;Ads Awdsâ;1 Bethesda, Galilea, Impe Mkals;29;63 
 
 264;16 October 1978;2 April 2005;AAz Jgfg adal II;Madwl Qózca Asdtyła;20 May 1920 Maklo, Polasn;58;84
I tried to find the space using anything ranging from regex to \zs but failed. Closest I came was finding the 5th colon. 

 %s/\(.\{-};\zs\)\{5}/;/g
But i need to find the space that comes after the number that comes after the 5th colon, so this kind of thinking got me nowhere and now I am trying to find the space in the the parts that i defined earlier. I feel like I could do this with awk -F but I need to learn to find a way to set delimiters and change a character of nth region in vim.