I'm assuming you want only **1-dimensional movement**; movement in a straight line. 

As you say, `s = ut + a*t*t/2`, where `u` is initial velocity, `a` is acceleration and `t` is time. Rearranging for `a` gives `a = 2*(s - u*t) / (t*t)`.

To arrive at a different time, just substitute a different value for `t`. To get a feel for how it works, you could [try it on Wolfram Alpha][1].

Note that if your physics are using approximating reality by running a calculation every step rather than actually following a differential equation curve (i.e. [Euler integration][2]), this won't *quite*  match up. (Though with small and frequent steps, it's really close.)


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**Edit**: So how do you calculate how long the ball takes to get there *in the first place*? It's a little harder, since `t` is quadratic, but it's still high-school maths.

Here's a sketch:

![How you might go about calculating the initial time][3]

Now we could substitute the red equation for `t0`</sub> into that last equation for `a`, but it would get messy.

I'd recommend just working it out in two steps like that.

To reiterate:

 1. Use your known values to solve `s = u*t0 + a*t0*t0*/2` for `t0` to get the time the ball takes to get to its destination.
 2. Rearrange `s = u*t + a*t*t*/2` to solve for the new acceleration value `a`.
 3. Substitute `t0 + desiredDelay` for `t`.
 4. Solve for `a`.


  [1]: http://www.wolframalpha.com/input/?i=suvat&a=FSelect_**SpeedAccelerationTime.DistanceSpeedTime-.SpeedAccelerationDistance.SpeedAccelerationDistanceCircularForm.AverageSpeed-&a=*FS-_**SpeedAccelerationTime.a-.*SpeedAccelerationTime.v-.*SpeedAccelerationTime.t-.*DistanceSpeedTime.d--&f3=1%20s&f=SpeedAccelerationTime.t_1%20s&f4=1%20m/s&f=SpeedAccelerationTime.v_1%20m/s&a=*FVarOpt.1-_***SpeedAccelerationTime.v--.***SpeedAccelerationTime.vi-.*SpeedAccelerationTime.vf---.**DistanceSpeedTime.d-.*DistanceSpeedTime.v---&a=*FVarOpt.2-_***DistanceSpeedTime.d--.***DistanceSpeedTime.xi-.*DistanceSpeedTime.xf---.**SpeedAccelerationTime.v-.*DistanceSpeedTime.v---&a=*FVarOpt-_**DistanceSpeedTime.a-.*DistanceSpeedTime.vi-.*SpeedAccelerationTime.v-.*DistanceSpeedTime.d--
  [2]: http://en.wikipedia.org/wiki/Euler_method
  [3]: https://i.sstatic.net/vSoYB.jpg