• By default, MacJournal does make periodic backups of your main document. You can find the backups in the MacJournal Backups folder. Just go into MacJournal Preferences, click on the Advanced tab. In the Main Document section, click on Reveal in Finder. This will take you to the Backups folder where you can browse recent backups of your MacJournal data.
• Starting with version 5.2.4, MacJournal by default automatically makes a backup copy before a sync. In your specific case, this information should have been backed up immediately prior to syncing.
• Sometimes, entries that appear to have been lost can be recovered via the "Restore Entries" option in the Help menu. Select Restore Entries, and MacJournal will restore entries it is able to recover to a new journal called "Restored Entries"
I'm hoping that one of these mechanisms built into the MacJournal app itself will have allowed you to recover those entries, despite the fact that Time Machine was turned off at the time the issue happened.