When testing Activity Streams, new blog posts were showing up with timestamps that were way off. I found that when Streams is querying content from Confluence, every com.atlassian.confluence.pages.BlogPost object has a creationDate property with no time (i.e. the date is correct but the time is 00:00:00). The lastModificationDate property has the correct time, so we can probably work around this in Streams by just using lastModificationDate instead of creationDate for new blog posts.
This might be related to
CONF-17872 - that issue was resolved as "not a bug" on the theory that it had to do with different server time vs. user time, but that can't be true in this case because I'm running locally. Also might be related to CONF-21910.