UTC problem I can't solve

[Harry77]

Have you selected a Local Timezone in your site settings?
Is there a date.timezone entry in your server's php.ini?

Local timezone in my site setting is Europe/Amsterdam, then I setup php.ini timezone "date.timezone = "Europe/Amsterdam"" and restarted httpd,

also, I have made the following:

timedatectl set-timezone Europe/Amsterdam

an the timedatectl output is:

      Local time: ven 2015-12-11 07:57:49 CET
  Universal time: ven 2015-12-11 06:57:49 UTC
        Timezone: Europe/Amsterdam (CET, +0100)
     NTP enabled: no
NTP synchronized: yes
 RTC in local TZ: no
      DST active: no
 Last DST change: DST ended at
                  dom 2015-10-25 02:59:59 CEST
                  dom 2015-10-25 02:00:00 CET
 Next DST change: DST begins (the clock jumps one hour forward) at
                  dom 2016-03-27 01:59:59 CET
                  dom 2016-03-27 03:00:00 CEST

So I think that I can say that the server timezone is correct and it matches the configuration of the site.

But now I got two different errors:

[11-Dec-2015 07:10:57 UTC] PHP Warning:  strtotime(): It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected the timezone 'UTC' for now, but please set date.timezone to select your timezone. in /home/admin/web/mysite.tld/public_html/plugins/news_manager/inc/site.php on line 353

line 353 is:

$date    = nm_get_date(i18n_r('news_manager/DATE_FORMAT'), strtotime($post->date));

and

[11-Dec-2015 07:10:57 UTC] PHP Warning:  strftime(): It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected the timezone 'UTC' for now, but please set date.timezone to select your timezone. in /home/admin/web/mysite.tld/public_html/plugins/news_manager/inc/functions.php on line 107

line 107 is:

    $date = strftime($format, $timestamp);

I installed many times getsimple+newsmanager and in many differents kind of server and control panel but I only had this problem with centos 7,
I admit to not being able to speculate on what the problem is but I seen this problem with this OS only so I think that the two things can be connected.