How long in general should it take an air pump ac or central ac to lower the temperature one degree? My heat pump ac takes one-half hour to do so. Is there an average time that is about right? Thanks.

It all depends on the heat capacity (in BTU) of the AC versus the cubicle content of the area the AC covers.
The bigger the number of BTU's the faster the inside temperature can decrease.

Another factor is the outside temperature : the higher that one is, the lower the overcapacity of the AC becomes to decrease the inside temperature, and the time increases.

Generally speaking, the supply air at the vent should be "about" 20 degrees cooler than the return air (room temp). If it's not cool enough it could be the reason that it taikes so long to cool the room. That being said, windows, insulation, air infiltration all make a difference in how long it takes to cool a space. If the supply air is not much cooler than the return air, the system simply will not work properly. Take a thermometer and note the temperature of the room... then lay it or hang it on a supply register and note that temperature. It's a good place to start.

Hope this helps.