Inserting-code-into-Execute-by-extending-BuildingBlockBase

I am writing some code for custom BuildingBlocks, as described in the ExtensionAPI here:
https://www.wealth-lab.com/Support/ExtensionApi/BuildingBlock

Is there any way to insert code at the top of the Execute() block, before evaluating conditions? Basically, I just want to make the first line of the Execute() function include this:

CODE:
if (someBooleanVariableIsTrue) { return; }

Or, to put it another way, I only want to enter or exit positions in a specific window of time. But rather than having to define and evaluate this window of time repeatedly on every individual building block of the strategy, I just want to check a single time, at the very beginning of Execute().