Those sorts of things you typically would want to do as some sort of Statement of Work (SOW) you build based on some consulting or at least a good grilling session to pick out what they have, what they want, and determine how long you'd need to do it, complete with contingencies. You could do it as a fixed-price and scope, but those never work out well for you mostly, as you'll get caught up in customer BS in just getting straight answers out of most. If you have a nice, clearly defined template of what the customer needs to provide, including a full list of up-front needs as deliverables, but for either you need to be sure you can get in and out as quickly as you say you can, or both sides will end up losing in the deal.
Even if inside your head you just expect them to give you information or *just* create some accounts, you never know what sort of politics and drama you might encounter to delay things. Go work for a 50+ year old company and see how long anything can possibly take, possibly weeks/months.
Best thing you can do is make a timeline as a literal project. I use MS Project to do so (one of the two M$ apps I love, aside from Visio), breaking out each and every action, request, receipt of request fulfillment, deployments, validations, dependencies, the whole works, including both reasonable timelines for completion. This then provides you a visible project timeline in the form of a Gantt chart even, but you can start with a baseline to then go and provide a list of every request up front to a customer, and let them determine how long they can fulfill each, then you can adjust your SOW, project, and timeline (and project costs) accordingly. ProjectLibre is OSS and also works as well, plus various online project saas' now, all come with some learning curve, but one more folks in the industry should know.
If the customer then delays you and thus the project unexpectedly outside your projected and documented timeline, your Statement of Work of course will (ahem, should) define and necessitate use of Change Orders they are responsible for in terms of overage costs and know that up front as projections were made on their direct input. If you did a fixed-bid project, you are thus screwed and eat their delay for whatever reasons.
Case in point, my last customer we had a project on the table to move various management services to Okta SSO for same reasons, but the IAM team was a mess that ran it with people coming and quitting as quick, and was in works for 7 months before I finally ran away from the mess, leaving it for their team and some other poor bastard to get around to implementing my documented requests eventually. At least it was all billable hours as staff aug more than pure consulting, so as they sat on their thumbs, I just went and did other work. It was the same there for a major network tool they purchased I worked on trying to get ServiceNow integration and Okta between teams. A week long project could easily become a 6mo to year long thing in some messes of organizations when consulting...
-mb