How much to run the pump

I have a 10X20 pond with a 35ft stream with 5 falls. How many hours a day should I run the pump? I need to trun the pump off to feed the fish otherwise the food get pulled into the skimmer.

Get rid of the skimmer and run the pump 24/7. This is not a swimming pool.

Personally I see no problem turning the pump off for 5 to 10 minutes while your fish feed. Otherwise, as DrDave says, the pump needs to run 24/7. The danger is in turning the pump off "just for a few minutes," and then forgetting to turn the pump back on. Without freshly ogygenated water, the beneficial bacteria in your filtation system start to die off quickly.

try feeding further away from the pump

I occasionally turn off my pump for the same reason; a few minutes will not hurt at all. Usually my fish will consume all the food before it reaches the skimmer, perhaps you are overfeeding? However, other than that, 24/7 is required.

No don't get rid of your skimmer.
I run my pumps 24/7/365
I took a piece of 1" Styrofoam and cut it about 3" wider than the throat of the skimmer and tall enough to touch the rock overhang on the skimmer and go about 1" under the water.each end is beveled to a 45 degree angle.
I put this in place before I feed and never get food in the skimmer.
I take it out after feeding and if I forget the fish will remove it for me and play with it.