#!/bin/ksh
awk -F ':' -v debug=$# '
$1 == "start" {
	hs = $(NF - 2) + 0
	ms = $(NF - 1) + 0
	ss = $NF + 0
	if(debug) printf("$0=%s\n", $0)
}
$1 == "end" {
	he = $(NF - 2) + 0
	me = $(NF - 1) + 0
	se = $NF + 0
	if(se < ss) {
		me--
		se += 60
	}
	if(me < ms) {
		he--
		me += 60
	}
	if(he < hs) he += 24
	diff = (he - hs) * 3600 + (me - ms) * 60 + se - ss
	if(debug) printf("$0=%s\n", $0)
	if(debug) printf("%02d:%02d:%02d - %02d:%02d:%02d = %d\n",
			he, me, se, hs, ms, ss, diff)
	printf("%d sec\n", diff)
}' business_file

end:dgnoeingwoit:25:07:2010:13:42:12
start:1second:across:midnight:23:59:59
end:1second:across:midnight:00:00:00
start:1second:after:midnight:00:00:00
end:1second:after:midnight:00:00:01
start:full:day:00:00:00
end:full:day:23:59:59

912 sec
2749 sec
2789 sec
1 sec
1 sec
86399 sec

$0=start:skdjh:22:06:2010:10:30:22
$0=end:siifneworigo:22:06:2010:10:45:34
10:45:34 - 10:30:22 = 912
912 sec
$0=start:srsdneriieroi:24:06:2010:11:00:45
$0=end:erfqefegoieg:24:06:2010:11:46:34
11:45:94 - 11:00:45 = 2749
2749 sec
$0=start:sdjfhsldf:25:07:2010:12:55:43
$0=end:dgnoeingwoit:25:07:2010:13:42:12
12:101:72 - 12:55:43 = 2789
2789 sec
$0=start:1second:across:midnight:23:59:59
$0=end:1second:across:midnight:00:00:00
23:59:60 - 23:59:59 = 1
1 sec
$0=start:1second:after:midnight:00:00:00
$0=end:1second:after:midnight:00:00:01
00:00:01 - 00:00:00 = 1
1 sec
$0=start:full:day:00:00:00
$0=end:full:day:23:59:59
23:59:59 - 00:00:00 = 86399
86399 sec