TIMESTAMP values are likely from Apple Core Foundation code based on an epoch of Jan 1, 2001 00:00:00 GMT.
Time Utilities - Core Foundation | Apple Developer Documentation
Core Foundation measures time in units of seconds. The base data type
CFTimeInterval, which measures the difference in seconds
between two times. Fixed times, or dates, are defined by the
CFAbsoluteTime data type, which measures the time interval between a
particular date and the absolute reference date of Jan 1 2001 00:00:00
Wolfram Alpha: January 1, 2001 00:00:00 GMT + 498586831.475129 seconds
Result: 4:20:31 GMT | Wednesday, October 19, 2016
Wolfram Alpha: January 1, 2001 00:00:00 GMT + 497469155.776235 seconds
Result: 5:52:35 GMT | Thursday, October 6, 2016
Prior answer (still relevant)
Without more context, you must look for conversions that make sense.
The integer part is a reasonable number of seconds, and the decimal places could represent microseconds.
Option 1: UNIX Epoch
Wolfram Alpha: 498586831.475129 seconds since unix epoch
Corresponding Gregorian time and date:
4:20:31 pm UTC | Saturday, October 19, 1985
Is a date in 1985 reasonable for that record?
Option 2: Alternate Epoch
Wolfram Alpha: 498586831.475129 seconds ago
9:43:46 pm EDT | Sunday, July 22, 2001
Perhaps, the field represented seconds since January 1, 2000 or January 1, 2001.
Option 3: Duration
Wolfram Alpha: 498586831.475129 seconds
15.799587725555 average Gregorian years
Is this amount of time relevant to the record?
EDIT: With your additional context (of the date being between 2007 and the present), "Option 2: Alternate Epoch" becomes the most reasonable, and this record occurs about 15.8 years afterwards.