If the association takes over 20sec, it is likely the rest of wifi usage is going to be painful too, and the user will start wandering around for better reception anyway.
If OTOH only the association is slow, and the rest of networking is reliable, it is a bug somewhere in the stack. And it should be rather fixed than worked around (by adding a configuration option, in this case)
"Make that thing configurable" is often a sign of "cult of workarounds". The cultists prefer enforcing endusers to twiddle settings randomly until things work, instead fixing the underlying bugs.