ActivityDate: Date/Time the transaction occurred with the merchant.
SettlementDate: (TransactionSettlementDate in transaction record) Date/Time the transaction money is moved to the FBO/Submerchants accounts after settlement. Usually the same as ProcessedDate but not always.
SubmittedDate: (SettlementDate in transaction record) Date/Time when funding instructions for this transaction were sent to processor to move purchase/refund money from FBO to submerchant accounts.
ProcessedDate: Date/Time when the transaction was sent for processing. This has nothing to do with money movement, just information.