I'd recommend using a Radius Authentication service like Purple WiFi as it can handle Bandwidth/Time limits which can be unlocked with pre-made voucher codes.
For example, with Purple you can allow 1 hour of Free use every day and have the ability to charge customers for WiFi access or provide a coupon to continue.
You can also limit the amount of data they use rather than set a time limit, eg: 1 GB per day.
Purple makes making a splash page easier and can even integrate with Social media.
Purple Wifi is free up to 5 APs.
If you're in Australia we can help you out with licensing.