Most likely.
Why do the last three chapters take up half the game's playtime? There are a couple of reasons:
The biggest one is that Chapter 11 is completely unlike the previous chapters. Without spoiling too much, it's a very open level complete with optional side-missions and plenty of spaces to explore that aren't strictly necessary for the main plot. The crystarium really opens up quite a bit in this chapter and you have the opportunity to farm experience to gain some substantial character power. Now, you could skip most of this and just rush through the story, but...
The monsters become significantly stronger starting in chapter 11, especially the large monsters and boss fights. If you try and rush through the level, you may find yourself woefully underpowered when you hit some of the bosses, especially in chapter 12 (where it's too late to go back and farm). If you want to try rushing anyway, I recommend keeping a saved game in chapter 11, just in case.
Chapters 12 and 13 are roughly the length of the other chapters in content, but 13 also provides you the ability farm experience or components to upgrade your weapons as you deem necessary. This also adds to your playtime.
Because of all this, most people will spend half the game on these last three chapters. And yes, the save file indicator is a good estimation of your play time as long as you aren't jumping back to previous saves.