Limit Orders are used when one wants to specify a price they'd like to buy or sell at, rather than accepting the current market price. SoFi Invest currently accepts Limit Orders during market hours, these are "Day" orders meaning they are only good for the current trading session.
SoFi Invest is working on Good 'Til Cancelled (GTC) Orders. Limit GTC Orders will remain in the market until they are canceled by the user. (There are some special conditions where they can be canceled automatically.) Currently, we do not have an exact timeframe for when GTC Orders will be released, so keep an eye out for updates.