Any time. I think the comment about FSL and jokers refer to Jim Wendler feeling that at that time, they were the best iteration of 531. Because he is constantly working with people it seems like 531 evolves based on how Jim observes various permutations to work in practice.
You could just do the original, basic 531 with one of the assistance templates and you'd still get good results. It's just that FSL with jokers is better in most cases.
Also, I believe that Jim Wendler himself has said that BBB is better suited to being used easier on, because as you get stronger it can quickly become too much. I only ran two cycles before I switched to FSL.
Just personally, I think it's a good idea to run an original 531 template first, especially if you aren't training with someone who's been using 531 for a while. That way, you get a feel for 531 - especially the plus sets - without having to think too much. BBB is great for that. Once you've got a handle on it, all the material in Beyond makes a lot more sense so you're better able to apply it.
It took me around five or six cycles to really figure out how I could lay my 531 out to suit me best. It worked well from cycle one, but now it's set out exactly how I like it.
To be honest, though, that applies only to assistance. If you go in and attack your plus sets with a vengeance, you'll get plenty out of 531 already without needing to really think too much about what assistance you're going to do.