Athena Appleton wrote:I kind of got the idea that Quirrell was travelling and came across Voldemort during the summer before, and that's why he wears the turban all year (I don't think he would have done that otherwise.) But he had already gotton the post of DADA teacher... actually, are we positive Harry's first year at Hogwarts is Quirrell's first year of teaching at Hogwarts?
I had a look in PS and Hagrid is introducing Harry to everyone in the Three Broomsticks they bump into Professor Quirrell. And there is the following quote
"Harry - 'Is he always that nervous?'"
"Hagrid - 'Oh yeah. Poor Bloke. Brilliant mind. He was fine while he was studying outta books but then he took a year off ter get some first-hand experience...They say he met vampires in the Black Forest and there was a nasty bit o' trouble with a hag - never been the same since"
I take this to mean he was already teaching at Hogwarts and took a year out in which he met LV and let him into his body. In which case this means LV was possessing Quirrell at the very start of term.