Actually it isn't that obvious. In Python the datetime class by default is not time zone aware. If you have users coming from multiple time zones the best universal way to handle this is store the time in UTC which the datetime class has a method for datetime.utcnow(). This is how UNIX does it internally and then warps the time to the local time of the user based on their environment variable setting. If you don't do this then time comparisons across users become a real bear to deal with. If you have all the users on one server it will be the server time that is used to fill the database fields if you use datetime.now() instead so you might be able to manage it that way. The browser client through Javascript knows the timezone of the client and without being specific I believe there is a way to get from UTC to local time in Javascript. So again it comes back to using UTC on the server for the least effort over all.
Hope that helps Ron