Both APIs have a lastModifiedDateTime property in the response. Unfortunately the 1st API, Search for site has an issue, the lastModifiedDateTime property is outdated. The 2nd API, Get site includes the correct date/time, but an information of the site (like the ID) is required.
In May I opened a case to report the issue and it was confirmed, also by a product team. In their answer they told me the solution is too complex, they have no ETA until when a fix is implemented. I recently checked the beta API, still the same issue.
For me it's a problem how to get the recent modified sites if the 1st API has outdated data, instead to check all sites. Is there an alternative solution?