The mechanics of the timing is as follows: The builder has a set time to work on the resource building. This set time is X amount of hours equal to the level of that resource building! So if the builder is set to work on a lvl 1 drill for example, the builder would work on that drill for one hour. If the builder was set to work on a lvl 10 mine however, the builder work work for 10 hours before automatically stopping. No matter what level the builder is set to work on, when he finishes his work, there is a 6 hour cooldown time before that resource building is allowed to be worked on again. Also, a builder can be told to stop working on a resource building at any time for no cost other than that building will immediately begin a 6 hour cooldown period just as if the builder completed his entire shift!
Thanks for your questions, I hope that this makes sense! Some of the details are not set in stone (I'm considering raising the 6 hour cooldown to something longer like 12 or a day). I'm glad that you like this idea!

