Dates are used to separate pieces of the chat history, but not for the "current" chat history. This:
has a really great description of what happens.
Patch link is not working anymore. Also current messages are separated with a divider line and old messages has a bit dimmer font color, which should be enough to separate new and old messages in the current history. Of course, if someone provides a patch for the current source, which will add data stamp for new messages, it can be added.
Adapted a patch from Niklas Schaefer from https://community.igniterealtime.org/message/183725#183725
Now Spark appends a date for coming messages if there is no a date stamp of that date already in the history.
This change is creating an issue that the sent and received messages are not shown when there is no older messages in the chat window (both regular chats and muc). So, commenting the patch code out and will leave it for someone with better java skills to fix.
This is the commit commenting the code: https://github.com/igniterealtime/Spark/pull/34/files
Reattaching the original patch by Niklas.
Actually it seems that at some point during 2.9.0 implementation it was done. Although i would put the old and current history divider in the one on one chat above the current date stamp. Also, still need to check if this works ok with offline messages. As offline message first appears with server's time stamp, which can be yesterday. But after reopening a window it will show up as received today.