Time limit items in your cart
I think Commerce Cart Expiration (https://www.drupal.org/project/commerce_cart_expiration) will do what you want. But I've only used to expire carts that are older...48 hours, for example. That works fine with cron, but for shorter periods, you'll need something else.

From the readme:

The module also provides a block which displays the time remaining. Its content gets refreshed by javascript just like a countdown. To show up the block, add the 'Cart expiration' block to your preferred region under admin/structure/block.
You can configure this blocks content on the block configuration page. Use the token [commerce-order:expiration-formatted] to get a format that can be manipulated by javascript.