PEG-silane treatment: why incubate for 18 hours at 60 degrees Celsius?
The binding of proteins (and cells) to glass (or silicon) surfaces can be prevented by coating the glass with polyethylene glycol (PEG) groups. PEG-silane is a reagent used to create this coating.  

PEG-silane (the image shows a methoxy- version) (image taken from here; no connection)  will coat glass surfaces because the silane portion (right hand end of the structure shown) will react with -OH groups on the glass surface.  

I can't help with the part of the question about time and temperature of incubation, but it seems longer and hotter than protocols I have seen. Perhaps the indium tin oxide (ITO) coating on the slides has something to do with it?