Blank in conference solution - asterisks

I have written a conference solution(os-centos 6.8,Asterisk 11.25.1) and defined DTMF detection in confbridge .conf file under dialplan_exec action to allow a user to escape from the conference and execute commands in the dialplan so that once the dialplan exits the user will be put back into the conference

In this if we define 2 digits like (11,12,13,etc) - when the user presses the first digit alone (eg he intended to press 12, he press only 1 and NOT key in 2) the system is pushing him out of the conference and after a timeout put his back to the conference . The system takes about 5 seconds during which the user is not in the conference- During this time, the entire conference bridge is blank , i am guessing all the other members of the conference are also kicked out. for 5 seonds the entire line is blank. This happens every time the user misses to press the 2nd digit defined in the dialplan_exec

Please suggest a solution for this . I want to have 2 digits only. Is there any place where we can defined such a way that he will be pushed out of the conferece only if he presses the 2 digits? Or any where time out can be defines for this?