JMA I have also spoke to Admin about this issue, and although they are looking into it, it will need careful thought to ensure it copes with all scenarios.
Using a simple example where you want to export 3kw over the 3 hr peak window. Spreading the export would mean a discharge rate of 1kWh. Now lets say your home demand is 500w in this period. Only 500w can actually be exported as the home is demanding the other 500w from the battery. This results in you exporting only 1.5kw by the end of the export period. If the home demand shot up to 2kw in this period, then only 1kw can be supplied by the battery and so 1kw starts being pulled from the grid at peak price which is not good.
Therefore the discharge rate needs to be high enough to export what you want whilst also meeting home demand to avoid expensive grid pull. Therefore spreading the export over the 3hr period will not work for some people and they would prefer the option to export as quickly as possible at highest discharge rate to ensure they have the best chance of exporting and meeting home demand from the battery. The export would then need to stop and Eco mode restored as soon as the SOC limit is reached or when the period ends (whichever happens first).
This is less of an issue for GivEnergy AIO batteries as you have a high 6kW discharge rate, but other inverters have a much lower discharge rate. If your discharge rate is only 3kW and you have a high home demand then trying to export and meet home demand may not be possible and the priority would be to meet home demand first and then export what you can from the remainder, knowing that you may not export entirely what you scheduled.
It certainly needs a fix but I'm not sure a one size fits all will work when it comes to scheduled export and you have to factor in how Growatt batteries are affected by this to which I am not familiar with. My initial thoughts were to give users two options for export method:
1) Export as quickly as possible at highest discharge setting, and then revert settings.
2) Spread export over entire scheduled period and set discharge rate high enough enough to meet both home demand and meet the export schedule.