The full answer
An MVP in 4 to 8 weeks is realistic when the first release focuses on one core user journey, a small number of roles and a few well-documented integrations. That is usually enough to put a product in front of real users or investors and learn from them.
Full products and enterprise platforms take longer because they cover more roles, more workflows, more integrations and more testing. Data migration from existing systems, approval workflows and reporting are common reasons a platform moves towards the longer end of the 3 to 6 month range or beyond.
Regulated sectors such as healthcare and fintech, and programmes that connect several existing systems, are delivered in phases. Each phase ships working software, so value arrives early rather than at the end of a long build.
Timelines also depend on the client side: how quickly feedback, content, test accounts and approvals arrive. Your proposal includes a milestone plan, and two-week sprints with demos make progress visible throughout.