I'm seeing these maybe once a day on my daemon logs:
[2013-12-04 18:15:20] EXCEPTION: (PhutilProxyException) Error while executing task ID 419064 from queue.
{>} (Exception) Trying to send an email before next retry! now=1386180920, next=1386180921 at
[phabricator/src/applications/metamta/storage/PhabricatorMetaMTAMail.php:357]
#0 PhabricatorMetaMTAMail::sendNow() called at [phabricator/src/applications/metamta/PhabricatorMetaMTAWorker.php:25]
#1 PhabricatorMetaMTAWorker::doWork() called at [phabricator/src/infrastructure/daemon/workers/PhabricatorWorker.php:84]
#2 PhabricatorWorker::executeTask() called at [phabricator/src/infrastructure/daemon/workers/storage/PhabricatorWorkerActiveTask.php:122]
#3 PhabricatorWorkerActiveTask::executeTask() called at [phabricator/src/infrastructure/daemon/workers/PhabricatorTaskmasterDaemon.php:19]
#4 PhabricatorTaskmasterDaemon::run() called at [libphutil/src/daemon/PhutilDaemon.php:81]
#5 PhutilDaemon::execute() called at [libphutil/scripts/daemon/exec/exec_daemon.php:112]
(I've added the timestamp in there to get a better look).
The time difference is almost always around 1-5 milliseconds too soon.
I've only ever seen it with regards to emails.