The 'a' in the first sentence is wrong. You can't have both 'a' and the 's in the same noun phrase. This is because 'a' is an indefinite determiner and 's makes the noun phrase definite. You have two options for a correct sentence. You can either say "I have a two-day holiday" or you can say "I have two days' holiday".

Actually "I have a two day holiday" is more common.

It should be "I have a two day holiday.".