Found this about corn emergence.
 http://www.cornandsoybeandigest.com/corn/growing-degree-day-variability-affects-corn-emergence
 I thought this part about emergence time between plants was interesting.

 

People often worry that non-uniformity of emergence will reduce yield. Plants that lag in their development tend to stay behind and often lose the competition for light, water and nutrients. Although it is not true that such plants end up as "weeds" – that they reduce the yields of remaining plants – the larger plants do not make up for the yield lost from the plants that get left behind.

Non-uniform emergence is a problem if it is related to factors such as seedling damage, soil crusting, or low seed vigor. However, uniformity is also affected by temperature (GDD accumulation rates), as is the time between planting and emergence.

"I suggest that we consider emergence to be ‘uniform’ if it occurs over the time it takes to accumulate 20 or 25 GDD, whether that is one day or five days," Nafziger says. "As with other aspects of corn development, basing events on ‘thermal time,’ or GDDs, works better than using time measured in hours or days. The practical effect is that, once it warms up, plants that emerged in 110 GDD and those that took 130 GDD to emerge will differ very little in their stage of development. Once we get to June, 20 GDD is only one day’s accumulation."