How many hours there are in a day of Venus?
To begin with, every planetary day continues from one sunrise to the next sunrise. This means that every planetary day has in it more or less the same amount of time. Although many of us would wish that Venus day was longer :), the reality of life isn't that good.
Every planetary day is composed of exactly 24 planetary hours. But planetary hours are different from what we used to think of as hours. If you take the timespan between a sunrise and the consequent sunset, it will be different on different days, right? In the summer, this timespan will be longer than 12 hours, it will be the longest around the 22nd of June. In winter, especially around the 23rd of December this daylight timespan will be much shorter.
Now, if you divide this timespan by 12, you will get the length of a 'day hour'. It will be longer than 60 minutes in the summer and shorter than 60 minutes in winter.
You can also take the timespan from a sunset to the consequent sunrise and divide it by 12 - you'll get the length of a 'night hour' which will be longer in winter and shorter in summer. So every planetary day consists of 12 planetary 'day hours' and 12 planetary 'night hours', and the summary length of it is close to (but not exactly) 24 civil (i.e. normal, non-planetary) hours.
Hope this helps...