I am a security guard and sometimes we have nothing to do, and I have some colleagues with me. Is it permissible for me to take a little rest i.e., to sleep for a short while, when my colleagues are there, and if there is work to be done they will wake me up, so that it will not result in my falling short in doing my job.
If the boss knows about that and does not object, then there is nothing wrong with that. If he does not know then it is better to tell him so that you will have peace of mind and you can be sure that there is no problem, because you are regarded as being employed by him so your time belongs to him.
And Allaah knows best.