I noticed that this topic was aired last November and Will stated that most systems do not have this function.
I have just seen a Youtube video of the new Octopus Flux tariff which allows discharge to the grid during the peak period of 1600 to 1900 and pays 47p/kWh during the 3 hours.
There must be some way, maybe a firmware update, of taking advantage of this tariff by providing a timed discharge setting similar to the timed charge setting? If this is not possible discharge will only occur if the battery has reached 100% charge and the solar panels are still generating power (therefore may work in summer).
Phil