Time variable inside the model

Hello, one of the euler’s is,

\partial_{c}U(c_{t})=\frac{beta(t+1)}{\beta(t)}\partial_{c}U(c_{t+1})(1-\partial_{k}f(k_{t+1})-\delta)

where,

\beta(t) is a function that depends on time (not \beta^{t}), but I don’t know how to included in the model using Dynare’s syntax. Suggestions are welcome.