Millisecond Forums

Dear all
In my experiment, I want to provide participants a textbox in which they have to fill in all words they remember from previously seen word lists. The total duration they get to do this task, is 5 minutes. Everything works fine, apart from the fact that participants shouldn't be allowed to press 'continue' before the 5 minutes are over. In a similar topic on the forum, I found that you could make use of 'isvalidresponse' to make sure participants can't advance. However, this only seems to work for Inquisit 5 and not for version 6. Or am I missing something else? Thank you in advance for your help! Here, I provide some code for clarification:

<text recallInstructions>
/ items = ("Recall as many of the words from all studied lists as you can.
You can either start each word on a new line, or add spaces or commas in between words. Your remaining time is:
You cannot press the 'continue' button before the 5 minutes are over.")
/ position = (50%, 10%)
/ fontstyle = ("Arial", 3%, true, false, false, false, 5, 1)
/ size = (90%, 10%)
</text>

<openended recall_overallgroup1>
/ stimulusframes = [1 = recallInstructions]
/ pretrialpause = parameters.recallDelay
/ ontrialbegin = [
    values.Recall = "";
    values.countCorrect_neutral = 0;
    values.countCorrect_low = 0;
    values.countCorrect_high = 0;
    values.countCritical_neutral = 0;
    values.countCritical_low = 0;
    values.countCritical_high = 0;
    values.phase = "recall";
]
/ size = (20%, 30%)
/ multiline = true
/ charlimit = 5000
/ position = (50%, 53%)
/ isvalidresponse = [openended.recall_overallgroup1.latency >= 300000]
...
/ timeout = parameters.maxRecallDuration
</openended>

<block recallscreengroup1>
/ preinstructions = (recallPhase)
/ bgstim = (clock.timerrecall)
/ onblockbegin = [
    values.RecallWordEstimate = "";
    values.Recall = "";
    values.nr_otherRecalledWords = "";
    values.countCorrect_neutral = 0;
    values.countCorrect_low = 0;
    values.countCorrect_high = 0;
    values.countCritical_neutral = 0;
    values.countCritical_low = 0;
    values.countCritical_high = 0;
    values.intrusionOther = "";
    values.lure = "";
]
/ trials = [1 = recall_overallgroup1]
/ onblockend = [
    values.nextList = "";
]
</block>