When I click on the sun in Guide8b it tells me that sunrise is at
5:20 CDT and sunset is at 20:21 CDT. My location is:

Long. W88deg 25' 5.2"
Lat. N43deg 2' 7.8"
Elevation 280m

I notice that other software packages seem to give consistently
different times for this event. For example, Occult3 shows the sun
rising 5 minutes later at 5:25 CDT, but gives the same time of
sunset. I have seen similar differences with other software
packages.

I know that refraction and other issues make these times at best
approximate, but 5 minutes seems like a big difference! What could
account for a 5 minute difference in the calculated time of
sunrise? Also, if the sun is already above the horizon when I click
on it is Guide telling me what time it rose today, or what time it
will rise tomorrow?