Passing a multiple value parameter using textbox

Good day! i am creating a report in Visual studio 2008 with using a cube and tried to create a button using a textbox. i am able to pass a one value to the parameter for "Time" and the format is this ="[Time].[Years Quarters Months Weeks Days].[Quarters].&[2012-01-01T00:00:00]" in the action button. but when i try to pass a 2 value or more the parameter wont accept. 

=("[Time].[Years Quarters Months Weeks Days].[Quarters].&[2012-01-01T00:00:00]" AND 
 "[Time].[Years Quarters Months Weeks Days].[Quarters].&[2012-04-01T00:00:00]")could you please give some advice so my parameter will accept 2 values and how can i fix this? 

thanks in advance!

best regards,

Jef