Fix AppStartInfo add timestamp bug

Timestamp was being added to the last record, but records are kept sorted newest to oldest so change it to add to first record.

Also added some comments and debug logs.

Bug: 338125667
Test: while logging each timestamp, compare reocrds list before and after start, manually confirm it was attached to the correct record
Flag: EXEMPT - day-to-day bugfix
Change-Id: I1aefe787ec2ba5a1df39f7cd65c0de481b0c5296