Admin timeout WAY too short... need longer! How?

Version v150, no upgrade, fresh install, only modules installed are Advanced Shipper and TinyMCE, all installed via FTP. I've customized a few CSS things (mainly the width of the shop and the side columns).
I've also disabled a lot of the blocks that were in the side columns.
Yes I've looked in the FAQ/Tutorials and searched the forum and haven't found an answer.
I even ran a Google search of site:http://www.zen-cart.com/ for what I was looking for.

I really need a much longer Admin session time. I timeout while writing EZ Pages, while adding products, etc... I was thinking 3 hours would be a good timeout length. But I can't figure out how to set this up.

I found this thread where people are talking about adding seconds like 10800 (which is the number I wanted to use) but where are they adding this? In the Admin > My Store > Admin Session Time Out in Seconds it says this:

"Enter the time in seconds.
Max allowed is 900 for PCI Compliance Reasons.
Default=900
Example: 900= 15 min "

And only offers 300, 600, and 900 as options. I can't get anything done in those short amounts of time!

Is there a way? I don't mind hacking a file somewhere if I need to.

http://www.zen-cart.com/forum/showthread.php?t=190630

I haven't tried this and don't recommend it, especially if it's important that your site be PCI compliant. None of us like the seemingly arbitrary PCI rules, but that's what we've got.

Personally, as long as I don't lose my work when it times out, I don't think having to log in every 15 minutes is any big deal.

My client's site only does PayPal payments (and personal checks) so I felt it was worth the risk to increase the timeout to an hour... if I hear enough reasons that it was a bad decision, I can easily enough revert back.

I have found an easier way! Simply stay on the "Who's Online" page. The page will refresh at whatever interval you set, all of which are shorter than the timeout limit.