Rollovers are generally a slow process, because none of the third party administrating entities want you to take money out of your accounts with them. That said, the money should be invested (on one end or another) for most of, if not the entire time. The investments remain in your current account (actively participating in markets) for the initial week(s) while the paperwork is processed, and then should be allocated to your chosen investments almost, if not immediately, upon receipt by Vanguard. To be sure there isn't any period where funds are converted to cash and missing out on market fluctuations, you can ask the current custodian for specifics on how they handle rollover funds.