A hydrostatically set packer is held against setting by a locking member that is made of controlled electrolytic material (CEM). After introduction into a wellbore and exposure to thermal or well fluid inputs the lock made of CEM dissolves or is otherwise weakened to the point where relative movement can occur for the setting of the packer with available hydrostatic pressure. The locking member can also be a shape memory alloy at least in part whose shape change allows the tool to set.