Your turf needs water when it is growing. New turf may require watering twice a day for the first week, then 2-3 times a week, then, after 3-6 weeks, once a week.
Once your turf is established, it is best to water it well before noon, so it will dry off before evening. During the spring and autumn, the turf will require much less water than the summer, and during the winter the turf does not need to be watered at all.
It is recommended that you use a sprinkler to water your turf, as hand watering is generally the least accurate.