Seems you need to show 3months of statements with ending balance of 500k, doesn’t say you need the balance for 3 months.
Search at the top of the group for others from DC and ask them what they provided.
London embassy is quick and seem to allow funds to be moved a few days before if you have a strong application. Other people applying at other embassies have been rejected and they believe due to the funds not being in their account long enough