The first story, St Valentine's Day, is set during Season One of Ats, sometime after Doyle's death and during that grey period where Wesely is around but not yet working for Angel. Of course it goes without saying that it is also set during Season Four of BtVS and Willow has not yet discovered the love of Tara but is still recovering from the heartbreak of losing Oz.
St Valentine's Day
St Patrick's Day