How to set time in odoo and compare with other time.

question:1---I have 4 fields early and also have one to many lines where there is list of date and time.
now i want to compare first item of list with fixed date and result goes to early.
for example:

i have list of datetime. now i want to compare first item of list with that fixed time.
list like=[01/02/2017 11:00:00] [01/02/2017 12:00:00] [01/02/2017 13:00:00]
from here pick first list item time only that is 11:00:00
and compare with fixed time which we will fixed like=10:00:00
now difference of both time goes to early field..
please anyone tell me how to do this.

question2:-----please tell me how to set any time(i.e. i want some fixed time 10:00:00). how to set in odoo.
becoz i tired this:-

from datime import datetime
@api.onchange("employee_is")
def _onchange(self):
fixed_time = datetime.datetime.now("%h,%m,%s","10:00:00")

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please tel me is this correct way to set fixed random time.