Accounting for daylight savings in rails webapp and iCal - ruby-on-rails

Question

Right, this is a bit confusing for me, so I'm going to try and explain from the top!
I have a rails web app. It's an internal company app and will only be used in the UK.
One of the things the app does is manage meetings.
Meetings have a date & time when they start. There's a date/time picker on the form which allows the user to pick the date & time the meeting is for. I save this date AS IS into the database. All meetings last 2 hours, so the end time is simply start + 2 hours.
Example:
2013-06-23 6:45PM in the form is stored in the db as 2013-06-23 18:45:00
2013-12-23 6.45pm in the form is stored in the db as 2013-12-23 18:45:00
Note that the first date is during Daylight Savings (BST) and the second is during GMT. I don't actually care whether it is GMT or BST: the meeting happens at that time, absolutely.
Inside the rails webapp, I simply print out the exact date & time from the DB - formatted nicely, of course!
Now, at some point I send an email to the organiser of the meeting, and the person they're meeting with. This email tells them the the date & time of the meeting etc, and also includes an iCal (.ics) file for them to put into their (Outlook usually, but also Apple or gmail) calendar.
The issue I am having is that (using the above examples) Outlook shows the meetings like this:
Meeting #1: Start: 23/06/2013 7:45pm, End: 23/06/2013 9:45pm
Meeting #2: Start: 23/12/2013 6:45pm, End: 23/12/2013 8:45pm
Note that it has adjusted the first one because of the BST/GMT thing.
The text of the .ics file contains this code:
Meeting #1:
BEGIN:VCALENDAR
...
DTEND:20130623T204500Z
DTSTART:20130623T184500Z
...
END:VCALENDAR
Meeting #2:
BEGIN:VCALENDAR
...
DTEND:20131223T204500Z
DTSTART:20131223T184500Z
...
END:VCALENDAR
So I am encoding the dates/times using the Z timezone (UTC). I understand this is why Outlook mis converting the UTC time into the BST time for #1 and leaving #2 alone (because GMT == UTC)
My question is: how do I stop this happening? I want the time the meeting is scheduled for to be the absolute, actual time, regardless of GMT/BST: 6:45pm
Should I be storing the date-times as UTC in the DB? How would this be done (I assume it would apply to all dates, not just meeting start dates). And how to re-convert them back into the actual datetime when I display them in the webapp?
Extra:
I have an entry in my initializers/time_formats.rb like this:
:ical => "%Y%m%dT%H%M00Z"
So dates come out like "20130623T184500Z". I use this when building the ics. And this I think is the issue - if the date/time is during BST I don't want to be using Z, but something else?

Answer 1

Your problem is your date/time format. You have:
DTSTART:20130623T184500Z
in your .ics file and this corresponds to 19:45 BST (as British summer time is UTC+1).
There are a few things you should do. First, you can simply remove the 'Z' from the end of your dates. This means that the times inherit the timezone of the calendar, or the underlying application.
This will work assuming that the machines which are running Outlook are all in the Europe/London timezone. If not, or if you want to be a bit safer, you should also specify the following after your BEGIN: VCALENDAR line:
X-WR-TIMEZONE:Europe/London
This specifies the default timezone for all dates which are not specified explicitly.
Finally, if this does not work for any reason then you need to define your datetimes explicitly. First you need to add a timezone definition for Europe/London to the calendar. The info you need is available at http://www.tzurl.org/zoneinfo-outlook/Europe/London.ics. Then you need to ensure that all datetimes are of the format:
DTSTART;TZID=Europe/London:20130623T184500
This last approach is the best, as it means that if your requirements expand to other timezones you will be able to handle them relatively easily.

Answer 2

Sorry to answer this myself, but in case anyone else runs into this here's what I found was the cause of my particular issue. Note that the answer above re timezones also makes sense!
My rails app is storing UTC datetimes in the DB (as is default)
But, it also thought it's own timezone was UTC, which also seems to be the default.
The upshot of that is essentially it was storing local dates, local to UTC anyway. Changing the app to know it was sitting in Europe/London made it so the dates in the DB are all now accurately UTC (meaning, they're an hour off if I'm currently in BST)
I can now use the Z datetime format in iCals, and outlook and the rails app both convert the UTC date back into the actual datetime for the viewing-user's locale (Europe/London for everyone at the moment). This is what I wanted.