zogt_besser –
1: This is exactly the case where Rav Moshe says it is allowed.
2: Even Rav Moshe agrees that there is no Issur of Yichud, but rather says it is a bad idea because they might go out somewhere far and be Misyached. IN this type of scenario (which both are expected to be in specific places at specific times) that is not a Chashash.