Not sure what development environment you are using. One thing that really seems to make a difference is raising the memory you allow your JVM to have during the build. For instance, in IntelliJ IDEA you can change the config file to greatly increase the RAM allowed the jvm, and also in Eclipse. Also, there's always the option of using an SSD instead of a standard hard drive which greatly increases the file I/O time (do they have SSD's for Macs?). The last thing would be to make sure you're running the most appropriate Ant target in build.xml. Although you have to be careful about it, sometimes you don't necessarily need a whole clean and build. On my Windows machine a whole clean and build might take 20 minutes but my distribution target only takes 5 minutes or so. That's on a 64-bit machine and giving the jvm I think 3GB. 2-3 hours sounds really slow, though. Labkey guys can probably give you some great advice on speeding that up.

There's definitely something wrong with your machine or settings. Our build time is of course highly dependent on number of cores (our build will use them all), their speed, and available memory, but the range for a rebuild on reasonably modern machines tends to be 5 - 20 minutes. I believe all developers at LabKey using Macs (MacBook Pro laptops) are in that range.

Please provide more information. What is your machine configuration (model name, number of cores, speed, RAM)? Please reboot and issue an "ant rebuild" from the command line (to eliminate variability introduced by your IDE) and report the time it takes. If it's still slow, can you tell which parts are taking a long time?

Of course a full rebuild is rarely needed during incremental development. "ant build" or "ant <module name>" should be sufficient in most cases. And you can configure incremental IntelliJ builds and hot-swapping for even faster incremental development (with some caveats). Also, the -DdevMode=true flag and gwt-user-override environment variable can be helpful. Our documentation explains all of these options:
https://www.labkey.org/wiki/home/Documentation/page.view?name=build

In your case, though, you have an underlying configuration problem that needs to be addressed.

Adam