Is there a way to extend the timeframe for processing credit card?

Hi All   We notice we get alot of 'time limit exceeded' from students trying to buy courses, and wondered is there a way to extend this time-frame a little bit, because although we send them an email about it, many lose interest and don't sign up for the course. PS can you email us a link so we can extend our support license, we can't seem to find where it is. Thanks!   Brent Havill