How to make your laravel command run two days in a week and twice a day?

I have a laravel 5 app. I want to run a laravel command twice a day in two days of the week. My attempt is as follows:

$schedule->command('supervisor:reminder')->weekly()->mondays()->thursdays()->twiceDaily(6, 13);

I don't get the reminder emails. What could be wrong?

via Chebli Mohamed