possessive case with time periods

[Kotfor]

As far as I know it is correct to use possessive case in the following examples

an hour's walk
a five minute's talk
six days’ time

I'd like to know whether it is acceptable to transform them into

an hour walk
a five-minute talk
six-day time

 

[emsr2d2]

As far as I know it is correct to use the possessive case in the following examples:

An hour's walk :tick:
A five minute's talk :cross: No, this should be "A five-minute talk".
[In] six days’ time :tick:

I'd like to know whether it is acceptable to transform them into:

An hour walk :cross:
A five-minute talk - :tick:This is the only correct form
Six-day time :cross:

emsr2d2

 

[Kotfor]

Thanks a lot. Could you point out the criteria you are guided by when sorting them out? I mean why is it ok to say A five-minute talk but it's not ok to say An hour walk

PS: I am sorry I confused, it should have been

a five-minutes' talk instead of - A five minute's talk