External data can be used to map temperatures on nodes, so along with the temperatures, you should have node locations on which these temperatures are applied as well. Looking at the third image, that does not seem to be the case. What you can do is create a separate text file for each time step, which will contain all the nodes for all boundary conditions and then scope the files to each time step using data view.
Alternatively you can also automate this process via python using ACT, something on the lines of:
Change Tabular Data Values of a Standard Load or Support (ansys.com)
-Aniket
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