You can do either. It does not have to happen exactly the same every day, but you might think of playing with the idea of occasionally going longer, challenging the body sometimes have a longer fasting period.
Whatever feels most sustainable – your intervention should a) feel trivial for you to adhere to; it should b) play along well with the demands of your social environment; while c) delivering the bare minimum acceptable weight loss benefit. Sure, the one or other additional fasted hour may add up to a tangible bit of extra weight loss over time, but what good will it be if you struggle to uphold your intervention over the long haul, or end up routinely overeating during your eating window due to feeling restricted.