There is no time limit for the conference call itself, but individual participants have a maximum call time of 8 hours each.
If participants wish to continue beyond 8 hours they can simply hang up and dial back in to the conference.
Please do keep in mind that some network operators change the way they bill for calls with a duration over one hour. If your operator operates this policy, our advice would be to hang up and re-join the call after 55 minutes have elapsed.