Most of the effects of administering testosterone (at least to men with clinically low levels) take weeks or months to appear. For example, interest in sex takes 3+ weeks to increase.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3188848/

And much of the impact of testosterone happens in utero (Young boys and girls have similar levels; behavioral differences are driven by in utero exposure.)

This study seems to test a very narrow area where testosterone could influence empathy