My file contains data like this:
85119.805: [GC pause (G1 Evacuation Pause) (young) 218M->81M(256M), 0.0159821 secs]
87180.697: [GC pause (G1 Evacuation Pause) (young) 220M->82M(256M), 0.0115120 secs]
Where the number at the beginning of each line is the elapsed seconds since the file was opened.
How do I ingest this into a date/time stamp?
You cannot. The best you can do is use DATETIME=CURRENT
in props.conf.