; More information about the Dial :
http://voip-info.org/wiki-Asterisk+cmd+dial; 30 : The timeout parameter is optional. If not specifed, the Dial command will wait indefinitely, exiting only when the originating channel hangs up, or all the dialed channels return a busy or error condition. Otherwise it specifies a maximum time, in seconds, that the Dial command is to wait for a channel to answer.
; H: Allow the caller to hang up by dialing *
; r: Generate a ringing tone for the calling party
; m: Provide Music on Hold to the calling party until the called channel answers.
; L(x[:y][:z]): Limit the call to 'x' ms, warning when 'y' ms are left, repeated every 'z' ms)
; %timeout% tag is replaced by the calculated timeout according the credit & destination rate!
dialcommand_param="|30|HrL(%timeout%:61000:00000)"
look for this section in a2billing.conf and do as it says change the time in the dialcommand_parm from "30" to whatever you wnat it to be