Exactly. You could be vulnerable to time correlation attacks. There was a student at an ivy league university who didn't feel like having classes that day so he wanted to prank for a bomb in the building. Logs into Tor from the library, leaves his message and then gets caught because the node he connected to belonged to the university's network. Although the admins couldn't see Tor's traffic, they could see that a specific computer from the library was connected at that time to the node and they could see that the prank message came via Tor. Putting 1 and 1 together, the guy was caught.