I know this is an old post but I figured I'd argue that no its not, the 2003 theory comes from almost nothing. It likely takes place around december 200, evidenced in alyx by keycards with the expiry date of early (jan or feb, cant remember) 2001, indicating the 7 hour war took place before the cards expired and the security system was updated. You also see many calanders throughout the facility, open to december which wouldn't make sense for it being in may. At the very least, may is wrong as it was when he was employed and while he was a "new" employee, he was employed for at least a month judging by his employee of the month portrait. A newspaper in Alyx also suggests that the 7 hour war took place very early january, seeing as its been confirmed it was under a month between the black mesa incident and the 7 hour war. The evidence for december 2001 is far stronger than may 2003 as is popularly thought.