Rails timezone cheat sheet do's and don'ts, from http://www.elabs.se/blog/36-working-with-time-zones-in-ruby-on-rails

timezone-do.rb

2.hours.ago # => Fri, 02 Mar 2012 20:04:47 JST +09:00
1.day.from_now # => Fri, 03 Mar 2012 22:04:47 JST +09:00
Date.today.to_time_in_current_zone # => Fri, 02 Mar 2012 22:04:47 JST +09:00
Date.current # => Fri, 02 Mar
Time.zone.parse("2012-03-02 16:05:37") # => Fri, 02 Mar 2012 16:05:37 JST +09:00
Time.zone.now # => Fri, 02 Mar 2012 22:04:47 JST +09:00
Time.current # Same thing but shorter. (Thank you Lukas Sarnacki pointing this out.)
Time.zone.today # If you really can't have a Time or DateTime for some reason
Time.zone.now.utc.iso8601 # When supliyng an API (you can actually skip .zone here, but I find it better to always use it, than miss it when it's needed)
Time.strptime(time_string, '%Y-%m-%dT%H:%M:%S%z').in_time_zone(Time.zone) # If you can't use Time#parse

timezone-dont.rb

Time.now # => Returns system time and ignores your configured time zone.
Time.parse("2012-03-02 16:05:37") # => Will assume time string given is in the system's time zone.
Time.strptime(time_string, '%Y-%m-%dT%H:%M:%S%z') # Same problem as with Time#parse.
Date.today # This could be yesterday or tomorrow depending on the machine's time zone.
Date.today.to_time # => # Still not the configured time zone.

From https://www.varvet.com/blog/working-with-time-zones-in-ruby-on-rails/

Not sure why but this gist seem to be shuffled/jumbled up, here's what's shown in the article:
DO

2.hours.ago # => Thu, 27 Aug 2015 14:39:36 AFT +04:30
1.day.from_now # => Fri, 28 Aug 2015 16:39:36 AFT +04:30
Time.zone.parse("2015-08-27T12:09:36Z") # => Thu, 27 Aug 2015 16:39:36 AFT +04:30
Time.current # => Thu, 27 Aug 2015 16:39:36 AFT +04:30
Time.current.utc.iso8601 # When supliyng an API ("2015-08-27T12:09:36Z")
Time.strptime("2015-08-27T12:09:36Z", "%Y-%m-%dT%H:%M:%S%z").in_time_zone # If you can’t use Time.zone.parse (Thu, 27 Aug 2015 16:39:36 AFT +04:30)
Date.current # If you really can’t have a Time or DateTime for some reason (Thu, 27 Aug 2015)
Date.current.in_time_zone # If you have a date and want to make the best out of it (Thu, 27 Aug 2015 00:00:00 AFT +04:30)

DONT

Time.now # Returns system time and ignores your configured time zone. (2015-08-27 14:09:36 +0200)
Time.parse("2015-08-27T12:09:36Z") # Will assume time string given is in the system’s time zone. (2015-08-27 12:09:36 UTC)
Time.strptime("2015-08-27T12:09:36Z", "%Y-%m-%dT%H:%M:%S%z") # Same problem as with Time.parse. (2015-08-27 12:09:36 UTC)
Date.today # This could be yesterday or tomorrow depending on the machine’s time zone, see https://github.com/ramhoj/time-zone-article/issues/1 for more info. (Thu, 27 Aug 2015)

For example, note that in the gist, Time.zone.today has the comment # If you really can't have a Time or DateTime for some reason. However in the article, Date.current has that comment.

Also Date.today.to_time_in_current_zone was only supported until rails@4.0.2. See https://stackoverflow.com/a/22959676