Hi there,

I'm wondering when to use "в" when expressing time the following way:
(in the sense of: "at XX:XX, they do..." - not "it's XX:XX o'clock now")

7:20
solutions of mine:
1. в семь часов и двадцать минут ...
2. в двадцать минут восьмого...

I can remember to have heard of a "30-minute-mark" (31, actually...), where you go with "без" and omit "в":

7:40 - без двадцати восемь
(without "без": 7:40 - в семь часов и сорок минут ...?)

The reason I'm curious is the fact that in one of the books that I'm using, they're not using "в" in the following case:
6:22 - Двадцать две минуты седьмого она вернётся ...

Where did the preposition go?
(In other sentences, they DO use "в" for instances until the 31st minute: В четверть десятого ...)
Error in my book?