"/api/1.0/recent/feeds" - Pass the unix epoch of the start time with ?since=[unix epoch] and the max count you want with &max=[count].
Example: GET https://api.podcastindex.org/api/1.0/recent/feeds?since=1599108339&max=100
This call returns the most recent [max] number of feeds that have updated globally across the whole index, in reverse chronological order since [since] timestamp. The update time is based on the publish date of the most recent item, not the publish date in the feed channel itself, since that value is so often unreliable. You can consider this as a sort of "firehose" for the index. Calling this endpoint once per hour would probably give you most of what you need.
Note: If no [max] is specified, the default is 40.
Note: If no [since] is specified, the default is 15 minutes ago.