We study the fluctuation of the waiting time τ in the restricted solid-on-solid growth model. The waiting time τ(x, h) is defined as the Monte Carlo time for the surface at position x to reach height h. In contrast to the discrete height h(x, t), τ(x, h) is a continuous parameter following the Kardar-Parisi-Zhang equation with a different sign of the nonlinear term. In d = 2+1, the variance Wτ2 (h) of τ(x, h) grows as h2β with β = 0.249 ± 0.004 (from L = 16384) and saturates at L2α with α ≈ 0.398±0.005, where L is the system size. The measured exponents satisfied the scaling relation α + $$\frac{\alpha}{\beta}$$ α β = 2.0 very well. Our result shows that β is consistent with 1/4.