Imported data & localization settings

I’ve run into this issue on a few sites which I have built and am trying to understand exactly what is going on behind the scenes.

We are pulling data from an external system in two different methods and both methods show incorrect dates. The first way is through a plugin which makes a webservice call the the system, and the second method involved importing the entries directly into the EE database. The system we are pulling information from stores published date for all of its entries at midnight on the day it was published.

09/21/2011 00:00:00 09/20/2011 00:00:00 etc.

When I use the format parameter to display the dates through a template tag they come out one hour earlier.(09/20/2011 23:00:00, 09/19/2011 23:00:00, etc). If I use the php date() function the dates display correctly.

The first time this issue came up I noticed that Daylight Saving Time in the localization settings was set to no, and changing this to yes fixed the issue. So I have made sure to set this on all subsequent sites.

I am beginning to wonder if there is something I am doing incorrectly when I’ve been importing this data. For the data import I am using

$data['entry_date']             = strtotime($row->publicationDate);
$this->EE->api_channel_entries->submit_new_entry($channel_id, $data);

$row is a database object from other CMS’ database. The plugin also does something similar

$meeting->meeting_start_date = strtotime($meeting->meeting_start_date);
$meeting->meeting_end_date = strtotime($meeting->meeting_end_date);
return $this->EE->TMPL->parse_variables($this->EE->TMPL->tagdata,$meeting);

With the end of daylight savings time approaching, I am concerned about what will happen if the daylight savings time switch is switched to no. If DST is turned off on November 6th will the the dates be an hour off again? How will it affect entries that were entered when dst was turned on will all of them be a hour newer?

I also have several sites each with a good number of users. Is there anything which automatically adjusts for daylight savings time or am I going to have to go through and adjust these settings manually? What if any side effects could we experience if we leave daylight savings time turned on all year round.