1. Something being "over" just means it's ended. When "over with" is used it feels impatient, like someone just wants to end something, or wants something to end already, as if they're tired of it. It also means something will be completely over--or that people will resolutely end it. Often "get" is used with "over with". For example: "I can't wait to get this busy week over with.", or "Get it over with!" (<Has the sense of just going for it and doing it, without any more delay.) 2. Technically, you need and "is" in there. So, "when this is over with", I guess. (It's a little hard to tell, since it's an incomplete sentence.) (By the way, sometimes 'over with' will come up when it has nothing to do with something completely being over/having ended. Like with "I painted it over with blue paint" (re-painted in blue paint) or "I went over with her to the store" (me and her went to the store together) and so on.)