I don't think frequency is the main factor for identifying spam on HubPages. I'm sure it's a part of their system, but I always assume that there is some program that checks for basic things like, spelling and grammatical mistakes (similar to MS word), how many links there are, how many times words are repeated, etc. Since they can't read every hub when it's posted, this mechanism does a lot of the grunt work. Of course, I'm just assuming all of this and I don't have any evidence to back up this theory. But I've posted 5-6 hubs in a single day before and there was no problem. However, I would recommend spreading them out over a few days. You won't be penalized for posting them all the same day, but you will be rewarded for showing consistent activity over many days. (Most likely in the form of your user hub score).