You can set your authorize.net settings in Zen Cart to authorize instead of capture.
It is not easy to automate the "capturing" process. It's possible, but the code is not currently built-in to Zen Cart. You'd need to to build the code to issue the capture call to authorize.net's servers, and then write a script to do the captures daily for transactions initiated 7 days ago.
It's possible, but will require custom coding to make it happen.
I suspect there's nothing against doing something like this in your merchant account TOS, as auth and capt are standard activities, even when automated.
You can certainly get started by switching to Authorize Only mode, and become familiar with the Capture procedures.
[insert standard disclaimer:] If you choose to hire someone to assist with coding, be sure to check out their reputation and demonstration of skill :)
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