fix pytz API calls

`tz.localize(datetime.now())` may peek a wrong tzinfo during end-of-DST ('fall back") transitions when the local time is ambiguous. To get the current time as timezone-aware datetime object, `datetime.now(tz)` could be used instead.

In general, `.astimezone()` can cross UTC transitions boundaries therefore `tz.normalize()` might be necessary as recommended in [`pytz` docs](http://pytz.sourceforge.net/#localized-times-and-date-arithmetic)