Well, that's hard to say. If we go by the Season 4 opener, then we see the sisters are in power during Discord's reign, but again we don't know how long said reign was. It could've been short like Nightmare Moon's attack was, or it could've lasted years.
However, with the way the Journal starts no mention is made of Discord. The biggest foe the sisters face is a dragon that stole the Crystal Heart, and that was pretty close to the end of the sister's section of the journal; which leads me to believe it was all before Discord started his reign of terror chaos.