Sadly there would be no reduction of holding times from the creation of a 3rd runway. Any freed capacity would be very quickly filled. Holding is a necessay evil to make most use of the runways. No holding - no maximum throughput. The only way to reduce holding is to mandate that airports can only operate at a a proportion of their theoretical maximum movement rate (I recon about 90% should do it). No airport will willingly do this as they want more flights and more passengers in order to pay for their heavily leaveraged businesses. Heavy-handed regulation is really the only way to achieve this despite £BNs being spent to reinvent the wheel to get better throughput.