Hi,
I think there will be a 'HTML item' solution possible.... I'll look into that one as I think the solution might be very usefull..... for now, a getting around solution....: First, you must be using two parameters for your period; the in_range on 1 parameter filter will not work in this solution.
Create a boolean variable which checks date_start prompt < date_end prompt. Use this variable for a conditional block to show a 'finish' prompt button. To activate this use a 'reprompt' button which you could call something like 'check values'...... Again, not the nicest solution but it works..... (just checked itÂ

) And yes, make sure you removed the standard prompt buttons from your prompt page....
Regards, wink