If you are invested in mutual funds, like most 401ks are, your fund will only "trade" at the price at the close of the day. In this sense, an order to sell plac

If you are invested in mutual funds, like most 401ks are, your fund will only "trade" at the price at the close of the day. In this sense, an order to sell placed Wed morning won't actually sell until after market close Wed. Then Thursday you place an order to buy a new fund and the buy takes place at the close of Thursday business. You don't fully know exactly how many shares of the new fund you own until Friday morning. Every 401k I've dealt with allows you to place the buy/sell simultaneously, so you really only have a one business day turnaround, but I wouldn't be shocked to hear that some don't allow this.