Can Visual Studio put timestamps in the build log?

Other option is to increase level of MSBuild verbosity.

Tools -> Options -> Projects and Solutions -> Build and Run -> 

Set MSBuild project build output verbosity to Normal. That will give you output like this:

------ Build started: MyProject, Configuration: Debug x86 ------
Build started 24/03/2014 08:46:18.
...
Build succeeded.

Time Elapsed 00:00:05.18

For VC++ builds you can enable build timing. Go to Tools->Options->Projects and Solutions->VC++ Project settings and choose the option for 'Build Timing'