Duration of insulin action is an important and often under-appreciated pump setting. If you have it set much shorter than the actual insulin duration then it will invite adding more insulin when it is not needed and cause hypos. Where I came to appreciate it was when I had some very bad lows between four and five hours after eating. To draw this conclusion, however, one must be satisfied that the basal profile is correct or close enough.
I've used various settings on my pumps over the years and have ranged from three hours to four and one half hours, my current setting. This is a personal and customized setting and I think it varies some within the same person from day to day. When I had my pump set to only three hours, I experienced more hypos due to stacking one dose on top of another. Too short of a duration will make you want to over-correct highs, send you hypo and then it's off to the roller-coaster.
I've used four and one half hours for my Apidra insulin for the last several years. It's been a pretty good setting for me. I can watch the effects of an insulin correction on my CGM trace when I'm not eating or exercising during the correction time. What I look for is when the slow downward trace levels out or even turns up some. Night-time corrections around 1:00 a.m. using a CGM facilitates this analysis since I'm not eating or exercising during this time.
Before doing this you must be sure that the insulin sensitivity factor is dialed-in. This is the blood glucose drop that one unit of insulin produces. Delivering insulin successfully depends on many interconnected factors and is as much an art as a science.
Wil Dubois writes for Diabetes Mine and he addressed this issue in a column last year. It may help you to read about why this setting is important and how some of the pump gurus advise testing for this parameter.
Be aware that the size of an insulin bolus will have an effect on its duration. Studies have shown that larger boluses will, all other things held equal, tend to last longer.