HELOC's are like any other loan - purchase or refinance - taking anywhere from 3-4 weeks on average to originate, process, underwrite, and close. As with any lending, YMMV and faster closings are always possible.
Credit unions (PenFed/SDCCU, etc.) are all fast movers and their loan terms are competitive. From what I've heard Chase has been getting them done in 2 weeks.
My .02c
SGIP