The AccelStepper library bases its acceleration profile on the number of steps and the acceleration rate, not on time. And it is designed to accelerate from 0 to the max speed and then decelerate back to 0 within the number of steps in a single movement.
You may be able to figure out a number of steps and an acceleration rate that has the by-product of producing the profile you require.
Alternatively it is not difficult to write your own acceleration code. The code in this link should give you a starting point.
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