Try something like this:
sample data: (timezone= utc/zulutime)
timestamps = ['2015-03-25 21:15:00', '2015-06-27 18:24:00', '2015-06-27 18:22:00', '2015-06-27 18:21:00', '2015-07-07 07:53:00']
for timestamp in timestamps:
time = datetime.datetime.strptime(timestamp, "%Y-%m-%d %H:%M:%S")
hr, mi = (time.hour, time.minute)
if hr>=7 and hr<18: print ("daylight")
else: print ("evening or night")