I tried to send a second pm 10 minutes after my first and it responded with the following message. "This forum requires that you wait 21600 seconds between sending private messages. Please try again in 20877 seconds."
Basically it sounds like there's a 6hr delay to prevent your account from sending spam PM's I'm assuming. Likely due to your post count being low and it being a new account. Contribute to the DP community with a few posts and I'm sure this issue will clear up on its own.
I think my limit got lifted to 300 seconds (5 minutes) after I made 10 posts, I think. Once I hit 25 posts it turned to every 60 seconds (1 minute). So just make a few more posts and you should be fine.