For clarification purposes:
Example Scenario 1: You crash on beach. You can Short Rest 2 times. You Long Rest. End of Day. You adventure by day in broad daylight only. No adventuring by night. Night is reserved for campfire dialogues, etc.
Example Scenario 2: You crash on the beach at 7:00:00. You move about and meet Shadowheart at 7:03:05. She joins your party after a dialogue that lasted 5 minutes and 10 seconds. It's now 7:08:10. You make your way around, explore some things, and then encounter the intellect devourers at 7:17:30. Your fight with them lasts 5 rounds (30 seconds). It's 7:18:00. You Short Rest. It's 8:18:00. You continue on through the game and after doing a bunch of stuff, you're just outside the Dank Crypt and you short rest again starting at 8:43:32. After short rest, it's 9:43:32. You do more stuff and finally, at 10:33:49, you decide to Long Rest. You regain spell slots and health and everything, just like present End Day. Time progresses to 18:33:49. Sun is now over in the western sky. It's getting late. It's almost twilight. You adventure some more. At 19:29:06, you arrive at the grove and battle. Afterwards, it's 19:30:11 because the battle took 11 rounds. You decide to short rest. It's 20:30:11. Sun has set. It's nighttime now. You do more adventuring. You short rest at 20:45:51. After short rest, it's 21:45:51. You adventure some more and finally long rest at 22:06:09. When long rest ends, it's 6:06:09 in the morning. It's still dark. Dawn hasn't come yet because dawn is at 7:00:00.
Example Scenario 3: You crash on the beach. It is day. You move about and adventure. You use 2 short rests. It's still day. You long rest. You regain spell slots, health, etc. It's night. You adventure about some more during the night. You use 2 short rests. It's still night. You finally long rest. You regain spell slots, health, etc. It's day again and you have 2 more short rests to use. Adventure by day. Use 2 short rests. It's still day. Long rest. It's night. Wash, rinse and repeat.
Example Scenario 4: You crash on the beach. It is morning. You adventure about, fight the devourers. You need a short rest. You take one. It's now afternoon. You adventure, take a short rest. It's night. You adventure. You have no more short rests. You need to rest again. The only rest you have left is End Day. You End Day. All health and spell slots, etc. are restored. It's morning again.
Example Scenario 5: You crash on the beach. You don't want to travel by day. You're a drow. You have sun sensitivity. You will get disadvantage on most rolls because it's broad daylight. You click on Day/Night button and it's night now. You get no benefits of waiting until night. You just wait until night. No spell slot restore. No health restore. Nothing. You literally just changed it from Day to Night. You adventure by night, use 2 short rests, and need to long rest. You long rest and it's day again. Full health restore, spell slots, etc. Ah, but you don't want to travel by day, just like before. So you click the Day/Night button and make it night again. You still have 2 short rests that day. You journey about and use both. Time to long rest again. You long rest and it's morning again. Wash, rinse and repeat.