When creating payments in Sunrise, by default it will take the date (timestamp) that the payment is actually created in Sunrise. However when booking bank transfers most of the time you will book these payments from a bank statement which is the actual date that the payment came into your bank account.
You can enable the possibility of selecting the actual payment date for Bank transfers with a setting: ALLOW_BANKTRANSFER_DATE , values YES, set at channel 0.
This will allow you to select the bank transfer payment date when creating the payment.