Builder cool down

In the tech tree there is a “reduction of builder cool down”, reducing the cool down after builder movement. What exactly is this talking about? What is “builder movement?”

In general movement cool down of heroes is meaningless since energy is the limiting factor.

When building or upgrading a tower, you have 2 cooldown timers.

The lower part is fixed, but the upper part is variable (the further from your alliance, the bigger the timer will become):

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The cooldown reduction will lower the upper part of those 2 cooldowns.