I believe I've posted something similar on a different thread. I said this to one of my russian friends, and he had no idea what I was saying. So I asked about 20 of my russian speaking friends. About 5 of them from Russia, 10 from Ukraine, and another 5ish from other former soviet states. Only 1 of the 20 had heard this phrase... and he said it wasn't common at all.
and the words are kinda put together so in до свидания the o is simply not stressed and pronounced kinda like ы while in до скорого the o is right before the stresst syllable and therefore pronounced like "uh" in "nut", like EmonaSheeran said. There are some crazy rules on how to pronounce unstressed vowels depending on where they are :D for those who speak german, this might be helpful http://www.grammatiken.de/russische-grammatik/russisch-aussprache-unbetonte-vokale.php#idfr#