Lexical decision task timing

Hi all,

I am creating a lexical decision task with priming and I need the following order in every trial:
1. fixation point on the screen for 300 ms then clears
2. prime word on the screen for 300 ms then clears
3. target word on the screen for 300 ms then clears -- crucially, as soon as the word appears on the screen the participants have 2000 ms to say whether the word is a word or not which means that the key press can happen either when the word is on the screen or for an additional 1700 ms after the word disappears

What I have now is the following: 

task test

table words

keys a l

show text "+"

delay 300

clear -1

show text @1  #this is the prime
delay 300

clear -1

show text @2 #this is the target
delay 300

clear -1

readkey @4 2000

But what I think this does is accept the key only after the word has disappeared, and I need for the 2000 ms to start as soon as the word appears. 

Any suggestion for how to achieve what I need?

Thanks.