I believe it means dated, meaning they were able to determine roughly how old those atoms are, presumably based on the age of the sediment in which it was found.
Here time resolved means not just dated, but having a definitive "shape" through time (the temporal analog to "resolving" an astronomical object to more than just a single pixel). As others have pointed out, supernova derived Fe-60 merely 'dating' to 2 million years ago was already known.[1]
Supporting quote from the abstract:
>Our results show that the (60)Fe signal onset occurs around 2.6 Ma to 2.8 Ma, near the lower Pleistocene boundary, terminates around 1.7 Ma, and peaks at about 2.2 Ma.
