This information is only available in the v1 source get API that I’ve seen (I do not believe these APIs are officially supported by SailPoint, use at your own risk):
This is Java epoch time in ms, so for a duration you can just subtract the two.
This information isn’t available in any of the v3/beta APIs that I’ve seen. Unfortunately this API also has to be called individually for every source since the /api/source/list API doesn’t return these values for some reason. This means if you want to list it for all your sources, it’ll take some time to run…