CropsGrowingMaster in blocks.xml has this line.
<property name="PlantGrowing.GrowthRate" value="63.0"/> <!-- setting 1 is erratic. Recommend 2+ for testing or use -->
So that would be how you determine how long it takes for a plant to grow

I think that's set to 63 real-life minutes as default, but haven't played around with it to confirm.
like this? where I set the harvest time, as I'm playing 120min, it takes 240min to get ripe.
<block id="259" name="plantedPotato1">
<property name="Extends" value="cropsGrowingMaster"/>
<property name="CustomIcon" value="PotatoSeed"/>
<property name="Shape" value="ModelEntity"/>
<property name="Model" value="Entities/Plants/potato_plant_sproutPrefab"/>
<property name="Collide" value="melee"/>
<property name="Stacknumber" value="250"/>
<property name="PlantGrowing.Next" value="plantedPotato2"/>
<property class="UpgradeBlock">
<property name="ToBlock" value="plantedPotato2"/>
<property name="Item" value="Fertilizer"/>
<property name="ItemCount" value="1"/>
<property name="UpgradeHitCount" value="1"/>
</property>
<property name="Group" value="Food/Cooking"/>
<drop event="Destroy" name="plantedPotato1" count="1" tool_category="Harvest"/>
</block>
<block id="260" name="plantedPotato2">
<property name="Extends" value="cropsGrowingMaster"/>
<property name="CreativeMode" value="Dev"/>
<property name="Shape" value="ModelEntity"/>
<property name="Model" value="Entities/Plants/potato_plant_growthPrefab"/>
<property name="PlantGrowing.Next" value="plantedPotato3Harvest"/>
<property name="Collide" value="melee"/>
<drop event="Destroy" name="plantedPotato1" count="1" tool_category="Harvest"/>
</block>
<block id="261" name="plantedPotato3Harvest">
<property name="Extends" value="cropsHarvestableMaster"/>
<property name="Shape" value="ModelEntity"/>
<property name="Model" value="Entities/Plants/potato_plant_harvestPrefab"/>
<property name="Collide" value="melee"/>
<property name="DowngradeBlock" value="plantedPotato1"/>
<drop event="Harvest" name="potato" count="1" tool_category="Crops"/>
<drop event="Harvest" name="potato" count="1" prob="0.25" tool_category="Crops"/>
</block>
Will this work? every 60 min = upgrade in the potato, 2 upgrade a total of 120min = 1 day in the game
<block id="259" name="plantedPotato1">
<property name="Extends" value="cropsGrowingMaster"/>
<property name="CustomIcon" value="PotatoSeed"/>
<property name="Shape" value="ModelEntity"/>
<property name="Model" value="Entities/Plants/potato_plant_sproutPrefab"/>
<property name="Collide" value="melee"/>
<property name="Stacknumber" value="250"/>
<property name="PlantGrowing.Next" value="plantedPotato2"/>
<property name="PlantGrowing.GrowthRate" value="60"/>
<property class="UpgradeBlock">
<property name="ToBlock" value="plantedPotato2"/>
<property name="Item" value="Fertilizer"/>
<property name="ItemCount" value="1"/>
<property name="UpgradeHitCount" value="1"/>
</property>
<property name="Group" value="Food/Cooking"/>
<drop event="Destroy" name="plantedPotato1" count="1" tool_category="Harvest"/>
</block>
<block id="260" name="plantedPotato2">
<property name="Extends" value="cropsGrowingMaster"/>
<property name="CreativeMode" value="Dev"/>
<property name="Shape" value="ModelEntity"/>
<property name="Model" value="Entities/Plants/potato_plant_growthPrefab"/>
<property name="PlantGrowing.Next" value="plantedPotato3Harvest"/>
<property name="PlantGrowing.GrowthRate" value="60"/>
<property name="Collide" value="melee"/>
<drop event="Destroy" name="plantedPotato1" count="1" tool_category="Harvest"/>
</block>
<block id="261" name="plantedPotato3Harvest">
<property name="Extends" value="cropsHarvestableMaster"/>
<property name="Shape" value="ModelEntity"/>
<property name="Model" value="Entities/Plants/potato_plant_harvestPrefab"/>
<property name="Collide" value="melee"/>
<property name="DowngradeBlock" value="plantedPotato1"/>
<drop event="Harvest" name="potato" count="1" tool_category="Crops"/>
<drop event="Harvest" name="potato" count="1" prob="0.25" tool_category="Crops"/>t="1" prob="0.25" tool_category="Crops"/>
</block>