Do you have any advice to jumpstart consulting engagements? It seems like, even with a reasonably well defined objective, the windup period is too long for my sense of urgency.

The responsibility for how long it takes a consultant and client team to hit their stride is the responsibility of both the consultant and the client. What you call the windup period is probably the least value producing period in an engagement. This is the period where you get to meet the client, get to know the culture of the organization, get caught up on company history, and become trusted enough by staff to hear the backstory on the specifics of your engagement. Unless you are starting an engagement with a past client, this stage, however long or short, is inevitable in each engagement.

If you think your are itching to get started with the engagement, imagine what your client must be feeling. The best thing you can do is to come to each engagement with a plan of action to get to work providing value as quickly as possible. The plan should include your best guess of what people, information, relationships, and authorities you need to get to work on day one.

Tip: Provide to your client a two-week (or whatever period makes sense for the startup phase) plan of what you need up front, what you want from the client as to ongoing support, and when you need it. Provide a written explanation that you don't want to waste anyone's time and describe the reasons you need specific types of data, facilities, support staff, access to prior internal or consultant analysis reports, etc. If staff interaction is a major part of the project, ask that your presence and role be announced before you arrive, that you be introduced to staff as soon as you arrive, and that staff have access to you as soon as possible. This comes off as thoughtful and professional, and gets you through the windup period a lot faster.