As per traditional rules Hindu temples is to be closed around 7:30 PM – an hour and a half after sunset. But this rule is not followed by most temples due to commercialization. Some popular temples nowadays remain open late into the night to accommodate the huge number of devotees.
The traditional belief is that once the sun sets humans are supposed to sleep. The deity never sleeps. But the deity roams around the area protecting its living beings from negative forces. Night is also the time when supernatural elements come out to hunt and eat. It is also the time when clash between the good and the evil take place.
Night is also the time for rest and recuperation. So once the sunlight is not present, then temples are to be closed.
Majority of the temples will remain closed during solar and lunar eclipses and will only open for darshan after 9 hours of the eclipse period.