bedtime前面的介词

前面用介词at，例如：

1.She says these activities at bedtime can get kids all excited and make it hard for them to calm down and sleep ．她说,这些睡前活动会让孩子们兴奋不已,让他们难以平静下来入睡。

2.For the greatest effect, please take this drug at bedtime.为更好发挥这种药物的作用，请在睡前服用这种药物。

3.Take one dose of the medicine at bedtime.就寝时服用该药一次。