Hi Eoin,
Within cBioPortal we also provide a clinical attirbute ('Tissue Source Site') which lists the site at which the sample was acquired.
In terms of when a sample was taken, it depends what you mean. As far as I know, the date of sample acquisition is not available. However, if your question relates to when a sample was taken relative to the patient disease course, that information is available for some patients, eg:
https://www.cbioportal.org/patient?studyId=paad_tcga_pan_can_atlas_2018&caseId=TCGA-2J-AAB1 TCGA was primarily interested in analyzing pre-treatment tumors, so in general the samples are not post-treatment.
Finally, I advise against analyzing two different versions of the TCGA data together. This is because the Firehose Legacy and PanCancer Atlas studies contain many of the same patients/samples, which can bias your results. I suggest using just the PanCancer Atlas study, as it reflects a more recent re-analysis of all the data.
-Tali