Addvice please

I am currently 5 x 5 and looking for a 8 x 5 (l x W) any advice on an only length routine and if so how long do you think will it take to reach my goal

Your girth is adequate. I suspect you will change your plan and add gaining a little more along your PE journey. Length only can be gained by manual stretching, hanging, or the use of an ads. Jelqing can give both lentgh and girth and the proportion of l to g gain varies dependant on technique.