Phpmyadmin feed a timestamp column with "0000-00-00 00:00:00"?
If you need to calculate with the timestamp field, you simply may use SELECT UNIX_TIMESTAMP(yourtimestampfield);. I decided to use this instead of the int(11) because of the built in function on update CURRENT_TIMESTAMP which shows this format 0000-00-00 00:00:00.

Also inside of mysql queries yo may use it the reverse way like UPDATE user SET logouttime = FROM_UNIXTIME(UNIX_TIMESTAMP(logintime)+3600) WHERE user_id = 12345;

Hope this helps.