Well, ladies, it all depends on the definition of darkness, as you probably can guess. First, please read the definitions of civil, nautical and astronomical twilight. Then check the sunrise, sunset and twilight times in Helsinki. As you can see, today there's less than two hours, when it's darker than civil twilight here. You might want to compare the times in Helsinki to the corresponding times at your location.

There's also a graphical almanac available showing the times of daylight, twilight and darkness in Helsinki throughout the year. The months and days are on the vertical axis, and the time of the day is on the horizontal axis. The cyan represents daylight (sun above the horizon), black is total darkness, and the three different shades of blue stand for civil, nautical and astronomical twilight. As we are now almost in the middle of the graph in the up-down direction, we can see that there's just a short period of nautical twilight soon after midnight. It's interesting to compare the graph of Helsinki to the corresponding graph of Utsjoki, located in the northernmost part of Finland. There the sun has been constantly above the horizon for almost a month now, and it doesn't set until late July.

In practice the sky above Helsinki doesn't get dark at all during the night any more. Last week I noticed that the street lights went on at half past eleven in the evening. The white nights are really fantastic, but unfortunately the summer solstice is just nine days away, and after that the nights will slowly turn darker again. It's equally sad every year. :(

I hope I answered your question thoroughly enough. ;)