People do one meal a day (commonly called OMAD) all the time and are fine. The important thing is to get enough calories and nutrients in your meal. But on 18:6 you do get to spread your calories out.
And you can workout in the morning and eat in the afternoon. Just make sure your body can handle it (there might be some adjustment time) and make sure you’re meeting your protein goal during your eating window.
The ratio can change and if we say it’s X:Y
X is hours of fastingY is hours of feeding
So if you’re doing 18:6, and you’re eating at 11pm at the end of your shift, you could eat up until 5am (probably still sleeping) and then not again until 11pm which is one meal a day.
Depending on how your job allows for breaks you may find it better to eat just before work and at lunch so you can get 2 meals in, plus some healthy snacks.
Or you could eat from 10am-4pm as your 6 hour window, work and sleep fasted. Whatever works.
Both examples above are still 18:6 but shifted so that you sleep during your fasting window and can eat perhaps smaller meals more regularly.
Personally I work 8-5pm and allow myself to eat between midday and 8, but often I push to a 2-4pm lunch and finish eating by 7pm.