If you have an iPhone you can set a timer on the phone and instead of a sound, you select "Stop Playing" and it will shut of whatever you are listening to or watching.

Same here. No clue why and doing a site search on the hoopla support site turned up nothing.

Did find this:
"If you can’t find help for your specific need among the Frequently Asked Questions here, then please email us at feedback@hoopladigital.com. We do our best to respond within 48 hours Monday-Friday. Please include your: Library name, library card number, a description of your issue or request."

I'm going to write them.

I keep setting the sleep timer on Hoopla, but then it just keeps blowing right through it. Am I doing something wrong? Last night it went for hours while I was in and out of sleep, but I’d only set it for 15 minutes.