Currently when you receive a first message this day in Spark and if showing short history is enabled, it will only divide older messages with a line, but new messages won't have a date stamp attached before them until you close and reopen a chat window with that contact. For some users this may be confusing, because older and new messages appear grouped under the same, older date. So maybe new days date stamp should be added when first message of this day is received and the chat window opens. All subsequent messages will be already grouped under that date, so this change should only affect first message of a particular date.
When implementing this, should take into consideration and test how it works with receiving offline message. because on receiving it will show server's date, but after reopening chat window it will show current date.