I don't remember it increasing curing time. Yes, I bought mine from NDA. I bleeds a lot. I never thought of just using it for a swirl, I'll have to try that. After my first bleeding mess it just sits in my drawer. Wish I could share some.
I can't speak for the Red Clay but I do know that my Dead Sea Mud soaps took a fair bit longer to feel "dry" than a 6-8 week cure. They felt cool and moist to the touch for a good 8-10 weeks. They're fine now but that did surprise me.
I use Australian Red Reef clay from NDA and a lot of other clays and haven't noticed a longer cure time.
I mix mine with water from the recipe before incorporating it.