Controlling the transient self‐assembly of (macro)molecular building blocks is of fundamental interest, both to understand the dynamic processes occurring in living systems and to develop new generations of functional materials. The subtle interplay between different types of physicochemical interactions, as well as the possible reaction pathways, are crucial when both thermodynamic and kinetic factors play substantial roles, as in the case of transient supramolecular assemblies. Clock reactions are a promising tool to achieve temporal control over self‐assembly in non‐living materials. Here, we report on the tunable association of poly(allylamine hydrochloride) (PAH) fueled by the formaldehyde‐sulfite clock reaction. The electrostatic interaction between the large macromolecules and the small, oppositely charged sulfite ions gives rise to micron‐sized coacervate‐like complexes. As the clock proceeds, sulfite is completely depleted and the complexes dissociate. However, under suitable conditions, a subsequent reaction between the polyelectrolyte and formaldehyde can lock‐in the preformed supramolecular structure, giving rise to covalently crosslinked colloidal particles.