Timing issue when API query includes modified_since

[Allda]

Hi,
I just found a bit weird behavior when making API call which includes modified_since timestamp.

Here is an example...
Let's say that some script fetches data from v1/errata/ API every 2 hours and so it sets modified_since = now() - 2 * hour. It can happen that it always gets an empty response even if a new advisory is released in that time window.
I tried to debug this weird behavior and I found a root cause. It is related to a timing issue between when an advisory is released and how often VMaaS update data (is it every 6 hours?).

When an advisory is released more than 2 hours before VMaaS updates data the API query always return an emtpy response.