I noticed that 29030400 is used very often in the Expires directives for static files.
Google recommends to cache this kind of files up to 1 year (1 month at least).
I did the math: 29030400 seconds = 336 days
That is about 1 year minus 1 month, so it perfectly falls in the recommended interval, but the question is why exactly 29030400? And not 31536000 seconds = 365 days for example? Just a blind copy/paste of a value that was set randomly in the old days? Or does it have another explanation?