The question is a bit vague, but I'm assuming you're asking for an upper bound on the gap between the smallest non-zero eigenvalue and the second smallest non-zero eigenvalue (ignoring multiplicity), let's call this number $E$, taking the supremum over all closed hyperbolic surfaces. If $\lambda_j$ is the $j$th eigenvalue, counted with multiplicity, then Otal has shown that $\lambda_{2g-2}>\frac14$. Moreover, Buser has shown that this estimate is sharp: one can find for any $\epsilon >0$ a surface with $\lambda_{2g-3}<\epsilon$. Now, I believe that in these Buser examples, one could actually arrange that $\lambda_1=\lambda_2=\cdots=\lambda_{2g-3}$, by adjusting the moduli (recall moduli space has dimension $3g-3$). If so, this would show that $E\geq \frac14$.

On the other hand, a result of Besson implies the maximal multiplicity of $\lambda_1$ is $4g+3$, so we know that $E\leq 4g+4$. There is some universal bound on $\lambda_{4g+4}$, since by the Margulis Lemma, there exists $R>0$ so that on a Riemann surface of genus $g$, one can find $4g+5$ disjointly embedded disks of radius $R$ (there is such an $R$ for any linear function of $g$). By Corollary 4.65 of Gallot-Hulin-Lafontaine, one has $\lambda_{4g+4} \leq \lambda_1^D(D_{R})$, where $\lambda_1^D(D_R)$ is the first Dirichlet eigenvalue on a hyperbolic disk of radius $R$. Thus, $E\leq \lambda_1^D(D_R)$. One ought to be able to get explicit bounds on $R$ and $\lambda_1^D(D_R)$ using computations of Margulis constants to get an estimate of $E$.

It is conjectured by Colbois and Colin de Verdiere that the maximal multiplicity of $\lambda_1$ equals the chromatic number of a genus $g$ surface, which grows like $\sqrt{g}$. Given Huber's result that $\sup \lambda_1 \to \frac14$ as $g\to \infty$, this would imply that $E_g$ is asymptotic to $\frac14$, where $E_g$ is the maximal difference between these eigenvalues for genus $g$ hyperbolic surfaces.

The question is a bit vague, but I'm assuming you're asking for an upper bound on the gap between the smallest non-zero eigenvalue and the second smallest non-zero eigenvalue (ignoring multiplicity), let's call this number $E$, taking the supremum over all closed hyperbolic surfaces. If $\lambda_j$ is the $j$th eigenvalue, counted with multiplicity, then Otal has shown that $\lambda_{2g-2}>\frac14$. Moreover, Buser has shown that this estimate is sharp: one can find for any $\epsilon >0$ a surface with $\lambda_{2g-3}<\epsilon$. Now, I believe that in these Buser examples, one could actually arrange that $\lambda_1=\lambda_2=\cdots=\lambda_{2g-3}$, by adjusting the moduli (recall moduli space has dimension $3g-3$). If so, this would show that $E\geq \frac14$.

On the other hand, a result of Besson implies the maximal multiplicity of $\lambda_1$ is $4g+3$, so we know that $E\leq \lambda_{4g+4}$. There is some universal bound on $\lambda_{4g+4}$, since by the Margulis Lemma, there exists $R>0$ so that on a Riemann surface of genus $g$, one can find $4g+5$ disjointly embedded disks of radius $R$ (there is such an $R$ for any linear function of $g$). By Corollary 4.65 of Gallot-Hulin-Lafontaine, one has $\lambda_{4g+4} \leq \lambda_1^D(D_{R})$, where $\lambda_1^D(D_R)$ is the first Dirichlet eigenvalue on a hyperbolic disk of radius $R$. Thus, $E\leq \lambda_1^D(D_R)$. One ought to be able to get explicit bounds on $R$ and $\lambda_1^D(D_R)$ using computations of Margulis constants to get an estimate of $E$.

It is conjectured by Colbois and Colin de Verdiere that the maximal multiplicity of $\lambda_1$ equals the chromatic number of a genus $g$ surface, which grows like $\sqrt{g}$. Given Huber's result that $\sup \lambda_1 \to \frac14$ as $g\to \infty$, this would imply that $E_g$ is asymptotic to $\frac14$, where $E_g$ is the maximal difference between these eigenvalues for genus $g$ hyperbolic surfaces.