This topic is my passion in life- in case you could not tell!
As far as melatonin goes, it is produced whenever you sleep basically. Production is suppressed by sunlight hitting the retina
. So if you are sleeping in a DARK room, you ARE producing melatonin during daytime sleep. Wearing sunglasses on the drive home- putting them on before you even walk outside the building, really helps with revving up melatonin production and sleep induction. Cortisol is secreted in exactly the opposite circadian pattern.
A person working days gets 'anchor sleep'. Anchor sleep is the 4-6 hour period of time each and every 24 hour period where a day worker is ALWAYS asleep. Midnight to 5 am for example. Anchor sleep is an important part of overall health.
The BEST approach to night work is staying on a night schedule 7 nights a week. Not practical for most of us, BUT it provides consistent anchor sleep. The NEXT best approach is to sleep 3-4am until noon-1pm on nights off. This allows you to have 'anchor sleep' as well.
I'm actually doing a pilot project educating newly hired night shifters on HOW to work nights, and a second project on how institutional practices impact the sleep of night shift workers.