这里的as they happen 有"发生"的意思
"it will send you suggestions with deals as they happen."
这句的意思是"网站会向你发送优惠建议当你输入你的日期"
as they happen 就是指前一句的 "you add your dates" 发生后，
输入好旅游日期(as they happen)，网站就会给你优惠建议(it will send you suggestions with deals)
这是我的理解> <，希望能帮助到你~