Hi @Livia1287,
The confusion you're experiencing happens because Airbnb counts nights stayed, not the days themselves. So, when you select 23rd to 28th, Airbnb counts it as 4 nights (the nights of 23rd, 24th, 25th, and 26th). The 28th is automatically blocked for check-out.
To have 2 separate trip lengths:
Set the first reservation to check-out on the 28th (so guests leave in the morning).
Then, make sure the next check-in is available from the 28th for the new guest to check-in later that day.
To do this:
Ensure your settings allow same-day check-out and check-in.
Adjust your availability in the calendar to open up the 28th for new guests after the first booking checks out.
This will allow guests to leave on the 28th morning and a new guest to check in on the same day!
Let me know if this helps!