You should probably change the format of the date you receive so that you datecan process it. I am changing it in format YYYY/MM/DD HH:MM:SSwith sed.
$ date -d"$(sed -r 's#(.{4})(.{2})(.{2})(.{2})(.{2})#\1/\2/\3 \4:\5:#' <<< "20140826225834")" "+%s"
1409086714
In parts:
$ sed -r 's#(.{4})(.{2})(.{2})(.{2})(.{2})#\1/\2/\3 \4:\5:#' <<< "20140826225834"
2014/08/26 22:58:34
$ date -d"2014/08/26 22:58:34"
Tue Aug 26 22:58:34 CEST 2014
$ date -d"2014/08/26 22:58:34" "+%s"
1409086714
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