Reducing audio delay for mixed mode delivery of audio transmissions

A system to reduce audio delay for mixed mode delivery of audio transmissions, the system comprising:

• a communication interface configured to be communicatively coupled to a communication network;
• and
• an electronic processor, coupled to the communication interface, and configured to
• receive, via the communication interface, a group call request for a talkgroup,
• transmit, in response to receiving the group call request, a call grant message to a plurality of subscriber units, the plurality of subscriber units affiliated with the talkgroup,
• determine, using a machine learning algorithm, a subset of the plurality of subscriber units based on a call grant response time;
• while a transmission hold-off timer has not expired, when a call grant response has been received from each of the subscriber units of the subset, forward an audio transmission to the subset based on the group call request;
• and
• update the call grant response time based on a plurality of historical subscriber unit response times, subscriber unit location data, and subscriber unit user metadata.