For a day job, we recommend that you don't take a nap after 3 pm. This is assuming that you go to bed at around midnight.
This means you can take a nap before going to work, or even on your break, as long as it's at least 9 hours before your bedtime.
Make sure it's not in your bed, it's for a maximum of 20 minutes, and that it reflects a need, not a habit. Planned naps are not a good idea. You don't know in advance how your day will go - whether you will be tired or not. If you are tired but it is no longer a good time to nap, there are other options. For example, relaxation techniques, getting some fresh air, or changing activities to avoid fatigue from repetition.