Here is a altered switchscript that should do what you want.
It opens the door that is typed in the IF USED field of the switch after 5 seconds:
;Header
desc = Switch Activates a Liftdoor after 5 Seconds
;Triggers
:state=0:hudreset,hudx=50,hudy=90,hudimagefine=gamecore\text\pressentertouse.tga,hudname=useswitchprompt,hudhide=1,hudmake=display,state=10
:plrdistwithin=50:hudshow=useswitchprompt,hudfadeout=useswitchprompt
:state=10,plrdistwithin=50,plrusingaction=1:state=1,plrsound=$0,TIMERSTART,alttexture=1
:state=1,plrusingaction=0:state=2
:state=2,TIMERGREATER=5000:state=3,activateifused=1
;End of Script
This scriptversion will only work once. After that the switch can't be used again.