Before you finish revising your WIP, please do the following:
1) Decide the time frame for your novel including the backstory. For example, novel takes place from October 1-31, 2012 but there are many references to an incident that started in May 2011 and ended in June 2011. If you don’t have a specific time frame in mind, pick one anyway. You don’t have to actually give the dates in your novel.
2) Once you have done #1, Google the words “calendar October 2012” for each month you need. When you find the month (usually they’re posted in PDF format) click Print so you have a print copy of the calendar.
NOTE: If you don’t want to Google & print, go find an actual calendar and photocopy it.
3) Once you have all of the months you need, go through your book and write down every chapter in the box for the day/days it spans. Do the same for the important elements of the backstory.
4) With your calendar on the wall or table in front of you, read your manuscript. Every single time you refer to a date or an event with an implied date (for example, last week, last month, the last time I saw her), check the calendar to ensure the reference makes sense. This is especially important for backstory. If I have to read ONE MORE BOOK where a character has a baby 11 months after peeing on a stick, I will throw something hard at something fluffy.