Equity research/sales teams try to get changes in recommendation out while the market is closed, so that the changes can be communicated, and clients can digest the research prior to the next open. In that window prior to the open, direct access to the analyst is often ~auctioned to valuable clients who express interest. Clients value, and pay for this type of service. Nowadays release of research is carefully managed by compliance departments that are tasked with ensuring equitable distribution to the firm's client base and other research outlets.
Special circumstances sometimes prompt those same teams to make exceptions. For example, a company makes a surprise announcement near the open, and the stock makes an egregious move, the analyst may quickly issue a short note, changing his numbers and perhaps even his core view, so that the sales team can engage clients real-time. These types of mid-day upgrades/downgrades are usually swamped by reaction to the original public announcement however, and its generally a position an analyst does not like to be in. Ideally he is simply telling the sales force "I told you so" and referring them to prior research.