You can output the result of an expression using curly braces.
If you
int x; x=10; ...
and you set the trace point after x = 10 with the expression x = {x}, it will output x = 10 to your output window.
Just put an expression that gives you a timestamp inside curly braces, for example timestamp = {time (0)} (depending on which API you use to get the time ....
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