I’m of the thought of “the longer the better.” If you can swing 6, go for it.
I did a 5 day in May and it was enough to do everything I wanted, but I also felt a bit limited. Mostly limited because I wanted to eat at more places and be in the bubble longer. I ended up bailing on boma because I had such a blast in MK earlier in the week and I wanted to do a repeat. I didn’t have enough time to fit boma in somewhere else.
Also with a 5 day, you only get 4 nights, so planning night time festivities was a bit of a challenge. Should any of those nights have been rain-outs, there was no chance for a do-over.