I don't think the FP have timestamps in Geocaching API. You can get amount of FP per cache, cachers favorite caches, but not the time when they gave the FP. The dates are not visible in the lists either:
Only possibility would be to interpolate the giving FP with logging found (the first? FI log), but it would be significant amount of work and re-calculation to get these data. Though I quite like this idea.