Debugging scheduled javascript workflows

Do you have any limits on how often a scheduled workflow can run? I have the following simplified workflow code, and can't get it to work at all (no comments posted):

var entities = require('v1/entities');

exports.rule = entities.Issue.onSchedule({
 title: 'Deadline checker',
 search: '#Postponed has: Deadline',
 cron: '* * * * *',
 action: function(ctx) {
 var issue = ctx.issue;
 issue.addComment("Checking deadline...");

},
requirements: {
}
});