"Is time within a function being solved using ode45 linear"
Time is linear in the sense that the difference between 1 and 2 is the same as the difference between 2 and 3. But I suspect you are actually asking if the times where the ODE function is evaluated are linearly spaced, in which case the answer is "no": the time step size used for calculating the function changes with the behavior of the function (stiffness, etc) and the user/default options. These sample steps are definitely not linearly spaced!
"or are time steps able to be repeated?"
I don't see anything in the documentation that excludes that possibility.
