Make a file called epoch.rb in your project (I put mine in config/initializers). Use it to store constants that represent the times when big dev events happened. For example:
CART_RELEASE = Time.local(2013, 04, 22, 13, 45)
We released our shopping cart at 1:45pm on 4/22. Fast forward to today: some of our stats are messed up, for deals that were live across the cart release. I need to fix the stats, but I only want to do it for the affected deals. It's this simple:
Deal.where("starts_at < ? and ends_at > ?", CART_RELEASE, CART_RELEASE)
That was WAY easier than digging around in git.