I've plopped with my hair at that length with no problems so you should be fine.
As for plopping overnight, all I can say is give it a try. I personally don't like to do that but that's just how my hair is.
3a/3b spirals and the occasional ringlet
Products I use:
Tresemme Naturals Nourishing Shampoo
Tresemme Naturals Nourishing Conditioner
Matrix Biolage Hydratherapie Aqua-Immersion Creme Masque
Homemade FSG with Lavender EO & AVJ/water mist spray containing Epsom Salt, Lavender EO