You could try using the internal timer - something like this might work for you...
:state=0:hudreset,hudx=50,hudy=90,hudimagefine=gamecore\text\user\First_Message.png,hudname=first_message,hudhide=1,hudmake=display,state=1
:state=0:hudreset,hudx=50,hudy=90,hudimagefine=gamecore\text\user\Second_Message.png,hudname=second_message,hudhide=1,hudmake=display,state=1
:state=0:hudreset,hudx=50,hudy=90,hudimagefine=gamecore\text\user\Third_Message.png,hudname=third_message,hudhide=1,hudmake=display,state=1
:state=1,plrdistwithin=80,plrusingaction=1:state=2
:state=2:hudshow=first_message,hudfadeout=firstmessage
:state=2:timerstart,state=3
:state=3,timergreater=500:hudshow=second_message,hudfadeout=second_message
:state=3:state=4,timerstart
:state=4,timergreater=500:hudshow=third_message,hudfadeout=third_message
Cleaned up a mistake I wrote in the code. xP
