Public infrastructure under security restrictions faces a scheduling problem conventional tools miss: constraints surface only after affecting work, information fragments with no authoritative version, and reliability is not measured. Following design science, this paper develops a model coupling four-dimensional Building Information Modeling (BIM 4D) with the Last Planner System (LPS). A structured search retained 54 journal studies, and interviews with eight experts across the decision chain of Colombian military infrastructure were analyzed under the Gioia methodology, yielding 25 codes, eight themes, and three dimensions. Maturity is intermediate and heterogeneous: the schedule is a contractual reference, updating reports what has occurred rather than preparing executable work, and constraint lists carry no ownership. The model couples four LPS planning levels and a measurement loop to a BIM 4D layer anchored in a constraint register, each entry carrying an owner, a release date, and a status, under governance rules for escalation and access. It is a structure prepared for validation, not an implemented system. The reliability gap arises not from absent BIM or lean methods, but from their disconnection from each other and from institutional decision making.