The gelation timetgnecessary for a solution of functional (associating) molecules to reach its gel point after a temperature jump, or a sudden concentration change, is theoretically calculated on the basis of the kinetic equation for the stepwise cross-linking reaction as a function of the concentration, temperature, functionalityfof the molecules, and multiplicitykof the cross-link junctions. It is shown that quite generallytgcan be decomposed into the product of the relaxation timetRand a thermodynamic factorQ. They are functions of a single scaled concentrationx≡λ(T)ϕ, whereλ(T)is the association constant andϕis the concentration. Therefore, the superposition principle holds withλ(T)as a shift factor of the concentration. Additionally, they all depend on the rate constants of the cross-link reaction, and hence it is possible to estimate these microscopic parameters from macroscopic measurements oftg. The thermodynamic factorQis shown to depend on the quench depth. It generates a singularity of logarithmic divergence as the temperature (concentration) approaches the equilibrium gel point, while the relaxation timetRchanges continuously across it. Gelation timetgobeys a power lawtg−1∼xnin the high concentration region, whose power indexnis related to the multiplicity of the cross-links. The retardation effect on the gelation time due to the reversibility of the cross-linking is explicitly calculated for some specific models of cross-linking to find the rate-controlling steps in order for the minimization of the gelation time to be easier in the gel processing. For a micellar cross-linking covering a wide range of the multiplicity, as seen in hydrophobically-modified water-soluble polymers,tRis shown to obey a formula similar to the Aniansson–Wall law.