Is it possible to visit Alhambra in the daytime and then revisit at night on same ticket?
Don't think so - they sell separate night time tickets. Afternoon tickets go until 8 p.m., then you have to have a different ticket at night. See http://www.alhambra-patronato.es/index.php/Ticket-sale/49+M5d637b1e38d/0/
NO -- one time entry only.
Two different tickets as you'll see when you order them online. I've seen the Alhambra both during the day (several times!) but only once as night - and it is impressive! Saludos, GranadaMan/MadridMan @ you-know-where!
A little footnote here: a night time visit is to see the impressive lighting which may be seen from other locations in Granada. It isn't actually necessary to be on the grounds.