As for media reports on welding at any given time and temperature, all I could say is just another pile of Bull$hit, you can't tell me that a media crew, with a thermometer was standing by as a welding team was carrying out, how many thousands of welds, on how many days, weeks on hundreds of k's of line, what would some young NumbSkull reporter know about the complexities of welding rail, more than likely been tipped off by Peter Walsh or similar trouble makers.
Alumnothermic welding is spectacular to those seeing it for the first time, even more so at night(!) few fail to be impressed, it's quite a show.
However the critical part of the rail adjustment process is carried out prior to the weld.
The process entails:
Remove rail fastenings (or anchors for spiked track)
Vibrate rail to ensure it is sitting stress free
Cut out the correct amount of steel, according to the rail temperature and the length of rail being adjusted
Apply the rail tensors and pull the rail up until only the weld gap remains (literally stretch the rail)
Release the tensors after weld cools sufficiently.
Note; not all welds are adjustment welds. 'Free' welding is carried out until the desired length of rail for rail adjustment purposes is reached. The adjustment is performed then the adjustment weld done; move on and repeat; in the case of construction work, ad infinitum (seemingly).
Unless a reporter has someone on hand to explain (and reporter has mechanical aptitude to comprehend what they are being told), said reporter would not have a clue what was going on, but it does look spectacular!