The rule of thumb that I was taught for software delivery is to double it for every layer of management you have to deal with.

So if it's just you to a customer, 1 week becomes 2.

If it's you, reporting to your manager, to a customer 1 week becomes 4.

Although I generally don't apply multipliers this liberally, I do keep in mind how many stakeholders there are that can add uncertainty and friction to a project.