it just really confused me, I always thought it was 'on that day' but in the Bible it keeps repeating 'in that day'......... could the translation be wrong?

Oh and another thing, is 'the best in the land' grammatically correct? How about 'the best in the earth'?

just becoming so confused
The bible uses lots of odd/obsolete language.

'land' is here being used to mean 'country'.
Sometimes "in that day" means "in those times, in that era", not "on that day":

In that day, navigation was by no means as simple a thing as it has since become. It is true, lunars were usually attempted in India and China ships; ...