As a result, the posts will be shown in one big bunch, which can place them all at the top of your feed.
Unfortunately, there is no current workaround for this. Future pins, however, will arrive in your feed with the correct date stamps.
At first, you may want to set your post order to "Random" from the Feed Settings panel, to mix all of your posts up each time your feed refreshes (which depends on your plan level).
Otherwise, we'd recommend that you add your Pinterest source before you add other sources, so these posts do not dominate the top of your feed. Over time, the feed will become a good mixture of posts.
If you have any questions or need any help please email us at firstname.lastname@example.org