Is there a time limit for a line-up and wait?
We can get some idea of what temperature the pavement would be subjected to by looking at some data on different jet aircraft.

Older low-bypass turbofans produced higher exhaust temperatures over a larger area than new high-bypass turbofans. This is due to the high-bypass engines having more of the cooler bypass air mixing with the hotter core exhaust.

Manufacturers provide various data about their aircraft that can be useful for planning operations at airports. Included in the data are figures showing exhaust velocity and temperature for different throttle settings.

It should be noted that aircraft holding for takeoff clearance will be at idle power. The power will be increased only when cleared for takeoff, so the takeoff temperatures will be experienced only briefly.

Although hot air tends to rise, the 737 analysis notes that:


  The buoyancy effects are considered to be small relative to the exhaust velocity and therefore are not included.


The figures for the 707 show the exhaust contours starting at the engines. The highest temperature labeled is 200°F (93°C), though higher temperatures would be expected closer to the engines. At idle power the 150°F (66°C) contour barely reaches the tail and stays above the ground. At takeoff power, the 200°F contour reaches bast the tail, but the highest temperature in contact with the ground would be the 150°F. These figures do note "data not verified by test".

The figures for the 737 note that the contours were produced by computer analysis. These contours only start at the aft end of the aircraft. The engines on the 737 are located closer to the ground than the 707. The original 737-100 and -200 models have the highest temperatures. At idle thrust, the 150°F contour barely reaches the tail of the plane, though it may reach the ground closer to the engines. At takeoff, the 200°F contour extends past the tail, and definitely reaches the ground.

The DC-8 is similar to the 707. At idle power, only small contours are shown for 125°F (52°C). At takeoff power, temperature contours reach 200°F but only the 150°F contour reaches the ground.

Based on these temperatures, it does not seem that an aircraft sitting on the runway with engines at idle would cause issues with the pavement. On a hot sunny day, asphalt could easily reach 150°F or more.