How much value add is from raw land to land with approved plans?

[Prithvi Sri]

There is a property of 8 acres costing around 3.5M (approx 10$ or less per sqft for the raw land). I am pitched by the developer that if we can get the approvals for 180k sft area warehouse on the plot (the land cost then would be approx 24$ per sqft of constructed area) , we can sell the approved plans for approx 40$ per sqft.  Is this a reasonable assumption? Will a builder pay 40$ for something that cost only 24$ but without approvals? How long does it take to get the whole project (of getting approved plans)?