When people are moving entries into their diary from other places, they often wonder if they can backdate those entries to the correct date/place in their diary. The good news is that you can!
To backdate an entry, you must first be editing that entry, either the first time you are writing it, or editing an existing entry. At the bottom of the editing page, click on the Options dropdown:
When you look at the options, there is a Published On box that shows the current date and time (or the date and time that the entry was originally published).
If you click on the date in the box, you will see a popup calendar where you can change the Publish date for the entry. If you change that date to a date in the past, this will save the entry as that date and place the entry in the proper place in your diary.