Via Support:

“As per the current behavior, Timeline activity Call Duration field will have a null value when a merge occurs (between a Gong synced call and a manual Timeline activity) if the user who created the manual activity did not fill the duration field. However there is no workaround to avoid this scenario other than creating the manual activities after 15 minutes of Gong call.”

This introduces a large data quality issue, because the behavior of this merge is discarding duration values that we already have synced from Gong as an accurate value in Timeline, and instead chooses to prioritize null duration values. 

Why would the merge action prioritize a null value when a previously validated source of this data, direct from Gong, exists? We now have hundreds of records where the call duration is null, and we would normally have all of this data if the merge with another Timeline activity didn’t remove the values that were already there.

Please consider changing this merge behavior to always prioritize a call duration value in there is already one populated in one of the two activities being merged.