Ballinger clearly stated that he received no reply from UA175, which would be his primary concern
The other times become important when no response has been received. They allow you to track the messages progress, just like the header of an email message will tell you when each email server along the route passed the message along. Those other times would be listed in the full ACARS message log kept by ARINC - the same log that Knerr & Winter used in their audits. All we have is Ballinger's printer log, and no information telling us how United Airlines configured their messages.
On another note: