In Mosaic Order Entry, open the "advanced" drop-down and select IBKRATS as the destination. In the Classic layout, use the Destination field in the order line to select IBKRATS. IBKR ATS supports limited order types.
When you route to IBKR ATS you can elect to have the trading system reroute the order to SMART after it has rested on IBKR ATS for a user-specified number of minutes. Access this feature anywhere you can choose IBKR ATS as your routing destination, for example in the Mosaic Order Entry tile's Advanced panel when IBKR ATS is selected as the destination, and in Accumulate/Distribute when you check "Route to IBKRATS". Simply enter the number of minutes you want the order to rest in the field labeled "Reroute to SMART after..." You can define a preset number of minutes in Global Configure in the For Orders Routed to IBKR ATS section of the Stocks Preset.
NOTE: In Classic layout, stock orders routed to IBKR ATS use the Stock Preset number of minutes to rest on IBKR ATS. To change this value on a per-order basis, add the Reroute to SMART after field from the TIme in Force category (hold your mouse over the bottom row of order field labels at the top of the window and select "Insert Column), or use the right-click menu from the order line to select Modify > Order Ticket.
Find out more about routing to IBKR ATS on the IBKR ATS Order Types page.