Our minimum billing length is 15 minutes - so if you need only to speak for five minutes the call will be charged as if 15 minutes ($31.20). And if you need to speak for 16 minutes, the call will be billed at 16 x $2.08 or $33.28. So calls under 15 minutes charged at the 15 minute rate. And calls over 15 minutes are charged by the minute.
What time you do not use remains as a credit on your account which you can use for more telephone support - or cash it in on a regular purchase.