It will be useful to see the time which is spent for starting of Tx in case when all attachments starts it with TIL = SNAPSHOT. Each Tx in such TIL must get own copy of TIP's active part and this action can take non-zero time when the gap (Next - OAT) has a big value and we have many concurrent attachments.
Currently we can`t see any info about elapsed time on START_TRANSACTION event:
. . .
2014-06-06T08:38:04.3700 (12862:0x7f1f86065988) START_TRANSACTION
oltp30 (ATT_4291, SYSDBA:NONE, NONE, TCPv4:192.168.43.96)
(TRA_3513899, CONCURRENCY | WAIT | READ_WRITE)
2014-06-06T08:38:04.3710 (12862:0x7f1f86065988) PREPARE_STATEMENT
. . .