Importing feeds
When a new feed is added to Tumblr, its most recent post will be imported, followed by any posts added from that point forward. Tumblr skips any entries that are more than 2 days old.
The time between updates can vary greatly depending on the service. We try to crawl feeds once every hour, but we do respect each feed's "Time To Live" (TTL) declaration which may affect the update interval.