Question: Using a vector in piecewise

Is it possible to use a vector in the piecewise fuction? I have tried the following and other stuff but the the error below

timestep := <seq(1 .. 100)>;
piecewise(`<`~(30, timestep), 1);
Error, (in PiecewiseTools:-Is) wrong kind of parameters in piecewise

I have a time vector and would like to create a u(t), unit step fuction to "turn on" a function at a certain time. e.g.


Where u(t)=1 for t>turn_on_time and 0 otherwise.

TIA for help

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