Each project is unique, but it is very common for consulting projects to start with contracts of 3 to 6 months, sometimes up to 12 months. Projects can be full-time or 3 to 4 days a week. The duration of a project depends on the type and scope of the project, as well as the client's and consultant's schedules. Time commitments can range from one-day facilitations to multi-month projects.
Yes, in fact, we've seen invoices at the MBB level that are that short and simple. What are the consequences of this? Companies that bill by project by team tend to have fairly stable levels in the team: almost all team members have the same weight and have a say in the direction of the project. In general, you are encouraged to resolve problems quickly. The difference between MBB and other consultants is not the quality of their knowledge, usually, but the speed with which they obtain it.