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From: Eli Zaretskii <eliz@gnu.org>
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Subject: Re: How to subtract timestamp in elisp?
Date: Sat, 04 Jul 2020 14:39:01 +0300
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In-Reply-To: <87zh8fwn4u.fsf@gmail.com> (message from stardiviner on Sat, 04
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> From: stardiviner <numbchild@gmail.com>
> Date: Sat, 04 Jul 2020 19:11:29 +0800
> 
> I hope a function can subtract two timestamps:
> 
>     00:12:35 - 00:10:45 = 00:01:50
> 
> Is there some hints or suggestion like function name or Emacs library or package?
> Or can convert timestamp into another format then convert back to timestamp.

I think you should start with parse-time-string.