Asterisk Blind Transfer ${ANSWEREDTIME}

I’m working on cross server, blind transfer, billing all combined together.
I’m running into an issue when
User A login to Server 1
User B login to Server 2

When someone calls User A, talk for 45 sec, then blind transfer to User B and talk for 60 sec. I’ve tried to catch the hangup signal on Server 1 and hopefully I get the full ${ANSWEREDTIME}, 45 + 60 sec, but all I get is 60 sec in Server 1. Is there any work around I can get the full talk time in Server 1 so I am able to bill User A and User B correctly?