date: illegal option -- d, Find difference between two dates - shell

Question

I am trying to convert timestamps read from a file from string to date format so that I can find the difference of 2 dates/timestamps. most of the threads/discussions on web show usage of date argument '-d' to convert the string to epoch or to find the difference of two timestamps Find difference between two dates in bash
But it looks like my environment/OS doesn't support -d date argument. Below are the details of my env:
bash --version
GNU bash, version 3.2.52(1)-release (i386-pc-solaris2.10)
Copyright (C) 2007 Free Software Foundation, Inc.
uname -a
SunOS s01***** 5.10 Generic_147148-26 i86pc i386 i86pc
Sample dates read from file:
START_TIME="09/03/16 - 01:04:56"
END_TIME="09/03/16 - 05:10:44"
Code that I have tried
I have tried to mimic the below code from Find difference between two dates in bash
!# /usr/bin/sh
date1="Sat Dec 28 03:22:19 2013"
date2="Sun Dec 29 02:22:19 2013"
date -d #$(( $(date -d "$date2" +%s) - $(date -d "$date1" +%s) )) -u +'%H:%M:%S'
bash test.sh
date: illegal option -- d
usage: date [-u] mmddHHMM[[cc]yy][.SS]
date [-u] [+format]
date -a [-]sss[.fff]
date: illegal option -- d
usage: date [-u] mmddHHMM[[cc]yy][.SS]
date [-u] [+format]
date -a [-]sss[.fff]
test.sh: line 5: - : syntax error: operand expected (error token is " ")
I don't think syntax error on line 5 is the main culprit cause I didnot find option -d in my date's man page.
In response to comments:
>>> date --version
date: illegal option -- version
usage: date [-u] mmddHHMM[[cc]yy][.SS]
date [-u] [+format]
date -a [-]sss[.fff]
>>> date --help
date: illegal option -- help
usage: date [-u] mmddHHMM[[cc]yy][.SS]
date [-u] [+format]
date -a [-]sss[.fff]
>>> echo $0
bash
Even these arguments are not supported. Apologies if I am committing any silly mistake.
Could someone please give me the equivalent of -d for the env details shared above or a way to find the difference between two dates without using -d.
Thanks in advance

Answer 1

awk mktime has a decent chance of existing on your system:
#!/bin/bash
START_TIME="09/03/16 - 01:04:56"
END_TIME="09/03/16 - 05:10:44"
echo -e "$START_TIME\n$END_TIME" |
tr '/:-' ' ' |
awk '{print "20"$3" "$2" "$1" "$4" "$5" "$6}' |
awk '{printf "%s ", mktime($0)}' |
awk '{print $2 - $1}'
explanation:
echo both time strings
tr converts 09/03/16 - 01:04:56 to 09 03 16 01:04:56
first awk changes 09 03 16 01 04 56 to 2016 03 09 01 04 56
second awk converts 2016 03 09 01 04 56 to epoch time: 1457514296 and prints both on one line: 1457514296 1457529044
third awk subtracts first from second, giving difference in seconds: 14748
the awks could also easily be merged, but here i kept each separate for clarity.

Answer 2

According to the POSIX standard, date does not do date and time math for you. It gets or sets the system date and time, possibly with timezone adjustments. See date(1) and note the lack of a -d option (or indeed, any interesting options!).
The question becomes "How do we do date and time math without date?" The timestamps you provided do not have time zone information, so the usual behavior is to assume local time. Local time is bad. Seriously. Some time zones have crazy discontinuities or didn't meaningfully exist hundreds of years ago (e.g. most American time zones). So while you might be able to hack together a custom solution that works in your particular part of the world during the recent past, it simply will not be robust.
If you can get your timestamps into Unix time, you can just subtract them, and that will give you a mostly but not entirely correct answer. Unfortunately, to the best of my knowledge, that can't be done at the command line. Unix provides strptime(3) to do this from C (and from there you go on to mktime(3), as shown in this answer), but I don't believe there is any fully standard utility which provides a command-line interface for this. You may have to write and compile your own.
Correcting for leap seconds is difficult in the extreme because, to the best of my knowledge, POSIX has never provided a standard interface for finding out when leap seconds have happened in the past. Such an interface would require internet connectivity in order to remain up-to-date, which is likely a non-starter for a number of implementations. Without knowing more about your system and its capabilities, I simply cannot begin to guess at what will or will not work for your use case.