The grass I planted after getting the foundation dug up started growing at an insane rate in the past few weeks. The first time I cut it, it was like a foot long. I worked nearly a month straight with only 3 days off, so I just could never do it, and it was raining all the time anyway even if I could. Then a week after I finally got to cut it, it was nearly as long again. That was a few days ago, now it's starting to get there, I'll definitely have to cut it tomorrow.
For the first couple weeks after I put the seeds it was looking hopeless, especially because it kept raining and eroding the soil. But once it decided to catch, it really did not take long to thicken up.