Need help in Inix script for finding duration

I have a file with time in it. I need to find the duration between the timestamp by subtracting second row from third row and so on. and wherever it is more than 30 minutes it should display start and end time which have been subtracted

file :

00:44:11
00:44:11
00:44:13
00:44:13
00:46:51
00:46:51
02:46:58 
03:47:10
08:47:10
08:47:11

so as 7th row minus 6th row time 2:46:58 - 00;46:51 is more than 30 minute so these time stamps should get displayed.

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In addition to what Don said: Please explain what is Inix.