at least 100 years.
let me show why:
avp hosts:
5 guys in sacrificial chamber, miller, verheiden (spelling?), the 1st guy that got separated in the pyramid hwen it shifted (this one is a bonus cause we cant be sure).
so 8 hosts.
existing aliens:
grid, + 1st alien scar killed (with shuriken) + alien lex killed with scar spear + aliens that scar plasma shotted (at least 3) + alien lex killed with gun
makes 7 aliens, now then could only have escaped 2 when scar was plasma shotting around, there were more then that, also when lex kileld the last alien, there where plenty more then 3! (shoudl be grid + the one taht died + one that wasnt killed (from the remaining host))
also freein the queen shoudl only be 3 aliens (grid + teh one tat wasnt kilelçd yet at the time + the one from remaining host)....they were more!
i could follow the examples....
this means the aliens from previous hunts were there!