Explanation of the new section:

you have ten minutes to reach the end (you start at O-225, section ends at O-250. Your speed is increased, but entities are more common.) The section slowly collapses over the ten minutes. A cutscene will play when you approach the door (note: you have to be really close to the door, so that you can read the sign.)

Basically just The Ridge from Pressure or The Greenhouse from Doors but longer.

The sign was inspired by this warning at R-2 in Delusional Office: