For those of you who want to pursue this in more depth there is an excellent short book by Robert Hand, titled 'Night & Day' published by ARHAT, priced $10.95
Firstly, you can tell at a glance whether it is a diurnal or nocturnal chart. In a diurnal chart the Sun is above the horizon - that is it is in houses 12 to 7 inclusive. For a nocturnal chart the Sun is in houses 6 to 1 inclusive.
It's not clear historically whether this system based on Sect(ion) or the chart in which the Sun lies, is an alternative to the dignities by sign, or a complementary one.
Generally a planet is stronger - in the sense that it is more able to fulfill it's role, if it is in a section of the chart that matches its character - with the exception of the two malefics, Mars and Saturn because we would like them to be less malefic.
Jupiter and the Moon are quite straightforward - Jupiter is a diurnal planet because its characteristics are Hot and Moist (the Sun strengthens it's heat in a Day chart but at night it is colder than it would like to be. In a day chart it's warmth and moisture encourage growth (of all things) - in a night chart it cannot do this as easily.
The Moon is cold and wet (much more wet than cold) it is best in a night chat - where its reflective and nurturing powers can work.
At this point it is worth adding a further distinction - placement. Because Jupiter is a diurnal planet, it should be above the horizon during the day - this strengthens it still further and below the horizon at night. Thus Jupiter in say the 5th house in a night chart is a little bit stronger than Jupiter in the tenth.
Similarly the Moon is stronger in a nocturnal chart if it is above the horizon (12th through to seventh). And in a diurnal chart it should be below the horizon. Clearly it is possible for the Moon to be above the horizon in a day chart or below in a night chart, as anyone who has seen the Moon during the day should realise. So if you have a nocturnal birth with the Moon above the horizon it should emphasise the Moon in your chart. Even if it is below the horizon in a nocturnal birth, the Moon is still the Sect ruler - that is the Moon rules night charts and should be treated as stronger than the Sun.
For the Two Malefics, the situation is partly reveresed. Mars is Hot (very Hot) and Dry and therefore is more dangerous during the day, when it's heat can be harmful (the impetuous, agressive, ignoring danger Mars). So Mars functions better in the chart (from the point of view of the native) if it is cooled down. Mars therefore is treated as a nocturnal planet - the cool of night reduces its intensity. Virtually the same reason is put forward for making Mars ruler of Scorpio - it is cooled and moistened and thereore more amenable. So interpret Mars at night as a more focussed and controllable agression which will do less harm.
Saturn is very cold and dry. Saturn at night is thus even colder and therefore more dangerous - it introduces fear of action, melancholic thought, imprisonment in structures (real or of thought). Saturn during the day is warmed up and threfore brings out it's best - the disciplined, planned, steady progress - learning from experience, etc. Think of a lizard, at night it is totally reduced to inaction, in the day it warms and basks in the Sun.
The same point applies in terms of placement for Mars and Saturn. Mars is better in a night chart, it is better still if it is above the horizon in such a chart (and below the horizon in a day chart).
I'll deal with Mercury and Venus separately because their situation depends on where they are relative to the Sun.
I'll end here on one last point about position. There is a third element (though the weakest) to sect. A diurnal planet functions better in a traditional masculine sign (Fire or Air) and a nocturnal planet functions better in a traditional feminine sign - (Earth or Water) - though there is some dispute about this in the case of Mars, where the Greeks took Mars as a masculine planet and wanted it in a masculine sign.
If a planet is in a chart of its own sect, placed according to sect and in a sign of its own sect, then it is said to be in Hayz - a condition akin to being in its own sign. Thus Jupiter, in a day chart in the ninth house in Leo is in Hayz.
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