if((startTime - finishTime) > 15*60*1000))
error[] = 'You take too long';
Great release, yeah you should add something like "You have 15min to answer the questions".
My idea to make it is adding a column to player like "time" and then when they click "Star Test" it sets the "time()" and when they click on finish make a comparisson with the start time and the finish time
PHP:if((startTime - finishTime) > 15*60*1000)) error[] = 'You take too long';
EASY! OGOGOOGOG
Maybe JS is in these situation better?