Well It must be hard when you try to learn something new when you've been playing the same way and probably on the same bass for 40 years ...
In my case I took the 5 strings (and I think it took me like a month ) after 2 years of learning bass on a 4 strings. 8 years later I got my first 6 strings and it was like 2 or 3 weeks to get it. Because before I got the 5 or the 6 I already knew what notes would be where ... so it was quite fast.
It took more time with the five because I had to change my muting technic to do it. Only a beneficial move.
In my case I took the 5 strings (and I think it took me like a month ) after 2 years of learning bass on a 4 strings. 8 years later I got my first 6 strings and it was like 2 or 3 weeks to get it. Because before I got the 5 or the 6 I already knew what notes would be where ... so it was quite fast.
It took more time with the five because I had to change my muting technic to do it. Only a beneficial move.