Dynamically Inserting Additional Content Items Targeting A Variable Duration For A Real-Time Content Stream

A content replacement system identifies regular content replacement parts and alternative content replacement parts, each alternative content replacement part being a content item with a duration within one of a plurality of ranges. The system detects a start of a content replacement break in a listener content stream, the listener content stream shifted by a listener delay value from a live content stream. The system inserts the regular content replacement parts into the stream. The system detects an end of the content replacement break for the listener content stream, and selects one of the alternative content replacement parts to insert into the listener content stream, the selected alternative content replacement part having a duration that when inserted into the listener content stream minimizes a difference between the listener delay value and a target delay value.