If you are wanting to mod the time they take to build you need to alter the additional time the pioneer kit causes them to take.

From CoreAccessories.xml remove the line in red below and the unit should take 3 turns to build. In theory making it -2 would make it take one turn to build. Not tested it though 

<!-- ************ -->
<!-- ** Packs ** -->
<!-- ************ -->

<GameItemType InternalName="PioneersKit">
<Type>Accessory</Type>
<!--Equipment Display Name/Description-->
<DisplayName>Pioneer's Pack</DisplayName>
<Description>The Pioneer's Pack is necessary for units to found new settlements.</Description>

<IconFile>Pack_Pioneer01.png</IconFile>
<IsAvailableForSovereignCustomization>false</IsAvailableForSovereignCustomization>

<!--Item Equip Information-->
<CanBeEquipped>1</CanBeEquipped>


<Weight>8</Weight>
<EquipSFX>Equip_Cloak_01</EquipSFX>
<EquipSFX>Equip_Cloak_02</EquipSFX>
<EquipSFX>Equip_Cloak_03</EquipSFX>
<EquipSFX>Equip_Cloak_04</EquipSFX>


<!--Equipment Production Requirements -->
<ProductionRequirement>
<Type>Resource</Type>
<Attribute>Gold</Attribute>
<Value>10.0</Value>
</ProductionRequirement>

<ProductionRequirement>
<Type>Resource</Type>
<Attribute>Materials</Attribute>
<Value>1.0</Value>
</ProductionRequirement>

<AdditionalTrainingTurns>5</AdditionalTrainingTurns>

<GameModifier>
<ModType>Unit</ModType>
<Attribute>UnlockAction</Attribute>
<StrVal>BuildTown</StrVal>
</GameModifier>

</GameItemType>

Shouldnt it be enough to make a new .xml file and enter

<GameItemType InternalName="PioneersKit">

<AdditionalTrainingTurns>2</AdditionalTrainingTurns>

</GameItemType>

For a 2-turn Pioneer's Kit? (Might need to do -3 instead, depending on logic.

Actually, upon reading it (additional) you might want to make it 0. This should be a value that overwrites the original (otherwise we cant properly change it). So, writing

<GameItemType InternalName="PioneersKit">

<AdditionalTrainingTurns>0</AdditionalTrainingTurns>

</GameItemType>

should result in units not needing any additional time to be built when receiving a Pioneer's Kit.

Thanks, guys. Will check it out!

Hell yeah imma edit this to make it a total of 10 turns, slower expansion