When an account is in margin deficit, it is subject to liquidation in real-time.  Any and all positions can be immediately liquidated.  Automated liquidations are accomplished with market orders, and any/all positions in the account can be liquidated.  The system which determines whether an account is in margin violation is entirely automated, and governed by a mathematical algorithm.  Once an account is determined to be in margin violation, either the system will automatically liquidate positions based on a proprietary algorithm or, if market conditions are better served by  manual liquidations in specific instruments, then liquidation orders will be manually transmitted.  Liquidations can occur at any market interval, whether positive or negative for the account holder.