How long can I expect a chkntfs to run on 500 GB drive?

I put Win 7 on my gaming laptop and it kept giving me a dirty bit - kept starting with that disk check, so I looked around the web and followed directions to do a chkntfs . It would have been awesome if they gave some sort of progress indicator. It's a 500 GB drive at 7200 rpm - CPU is 2.26 Core 2 Duo (If that matters).

How long can I expect that to run?

It depends.

A full surface scan (performed if you specified /r on the command line) will take some time, especially if there are bad/iffy sectors on the drive. If all is well it will take as long as the drive would normally take to read everything so if you have a rough idea of how many Mbytes/sec it can read you can estimate the time taken with a simple sum like 500*1000/{speed-in-mbytes/s}/60 - just shy of three hours if it is proceeding at ~50Mbyte/sec. You can interrupt the scan, but if you start it again it will restart from the beginning.

Other parts of the scan can take anything from tens of seconds to tens of minutes. On a system drive it will be at least a minute or so and if you have a lot of content on the partition, especially if there are many small files rather than few large ones, it will take quite a bit longer. Again this can generally be interrupted but will have to be restarted from scratch if you start the scan again.