I was thinking I had been giving extra hard ones lately and thought this one might be too hard so I came back here and you had already posted the answer!
Here is the way I would have done the search although your way may have differed:
Click on Search above and then on Advanced Search
Fill in Persi & Alley as the username and specify Threads started by user.
Use Alley as the keyword and search titles only. My logic here is that I would have started a thread upon receipt of my new cat, not just made a passing comment in a post. But wait, you are not done yet!
Here is the link you would have found: http://www.thecatsite.com/forums/sho...ighlight=alley
This thread was began on January 14th and that is where you could have been tripped up unless you read the first part of the thread which states that Alley arrived last Friday. So using the calendar that everybody seems to have in their phones these days, you could ascertain the date of January 12th.