I have to backup all my chat history onto my computer which is simple enough with the "email chat history" feature but I need to add the time that each message was sent to the backup file.
You can turn on chat history within BBM and have it save history to SD card. History will be saved into separate files based on PIN (if you have SMS in BBM, filenames look different for those). You can save those files to your computer, which does include timestamp. The only side note is that BBM only keeps a certain amount of history, so it is possible for older entries to be purged out of the file. As long as you make backups, everything should be preserved.
Not sure where the files are stored on each OS version, but on my Tour (OS 5), they are in /BlackBerry/im/BlackBerry Messenger/{mypin}/history/
