As I understand it, and until told otherwise by DNROI, the mag retainers applys to before the start signal, unless otherwise stated in the WSB. All shooters, regardless of division, must start in a legal configuration per 5.2.4.
As an Open shooter they are not restricted as to placement of magazines as Production, Carry Optics, and Single Stack are..
So after the start signal they may stow their mags anywhere but their mouth.