Q:

Drop test with load cell: longer impulse on load cell than optically

I have been performing a simple drop test on a load cell using a golf ball, recording the impact using a Phantom camera as well as collecting the data from the load cell.  
The problem arises when you compare the 2 time measurements for the impact of the golf ball on the load cell plate.  The phantom camera gives an impact time  of approximately 0.65ms whereas the load cell reading from start to end gives a much greater reading (approximately 0.85ms) as seen in the picture - also the 2 gradients from start to peak and from peak to end differ significantly, which we know is not true during a golf ball impact.  

How do you explain the time readings being different?  
How I could go about getting a more accurate value from the load cell
that matches the phantom camera? 

I have also been calculating the impulse of the impact and comparing it to the area under the graph on the load cell readings to check that the force readings are correct, however I cannot determine if they are right - most likely due to the time reading being wrong. 

A:

Any real-world system has limited speed.  So, that something that is very fast (optics) measures a short event "shorter" than a slower, mechanical system isn't surprising at all. 
If your sensor is linear, then you can model the slowness and "memory" effect by what we literally call an impulse response, being convoluted with the input signal (which, in your case, is the force of the golf ball).  There's rich theory of how to model these; in Electrical Engineering programs, we are taught about this in lectures called "signals and systems", or the like.  
Now, these properties of real-world systems simply mean that the output of your load cell contains less information than the output of your phantom camera.  You can't fully reconstruct what you see on that, mathematically – one system is more band-limited than the other. 
What you can do, however, is try to correlate any impact with the best estimate for a true impulse response of the system you can get.  That's easy to do, but it requires you to estimate the impulse response – but maybe a bit of correlation applied to the load cell signal and a signal modeled from your camera data suffices as an estimator for the impulse response.