Differentiate between daily and user initiated builds

We have a number of plans/builds we have termed as "official". These are slower and do more operations than our CI builds.

We typically run official builds only overnight, and they take over an hour.

Analyzing the builds, we have determined that almost half this time is spent building help files, which vary little between daily runs, and are typically not critical when we are wishing to get a midday "official" build turned out.

What we would like is some property that differentiates between a scheduled build and a user initiated build, so we can skip the help compile during midday/user initiated builds.

This may already exist, and I just don't know where to get it, but we already property the build-number.txt file that bamboo generates, and this would be a natural location for us to grab this piece of data.