from django.utils.dateparse import parse_datetime
import pytz
s1 = '2012-05-03 00:00:00' # start time
s2 = '2012-05-03 23:59:59' # end time, together covers 1 day
la = pytz.timezone('America/Los_Angeles')
n1 = parse_datetime(s1) # naive object
n2 = parse_datetime(s2)
aware_start_time = la.localize(n2) # aware object
aware_end_time = la.localize(n1)
MyModel.objects.filter(timestamp__range=(aware_start_time, aware_end_time))) # 'timestamp' is a datetime field