they went to a restaurant to have dinner ( )the evening of October.理由

they went to a restaurant to have dinner ( )the evening of October.理由
they went to a restaurant to have dinner ( )the evening of October.
理由

they went to a restaurant to have dinner ( )the evening of October.理由
on
October后面还应该有个具体的日期吧,在具体某一天的早上、晚上、下午介词用on.

in，对于morning, afternoon and evening, 介词用in

on
记得上学时候这是被当做固定用法记住的
在一个月份里的某天某晚......只要看到月份了 介词就用on

on, 具体指定日期的早中晚用on