From their website:
"Should you be one of the lucky ones that is getting up to 10Mbps on your ADSL line speeds, please use your account responsibly, or else Internet Solutions will enforce their stricter user policy on your profile.
Express+ Uncapped: The services are offered in three line speeds; 384, 512 and 1024 Kbps and carry a threshold of 5, 10 and 20 GB respectively in a 10 day window. Should a product threshold be exceeded then the line speed (ie 384, 512 or 1024kbs) for the respective service will be halved from 8 a.m. and 8 p.m. during weekdays. For the period outside these times, the line speed will be restored to full line speed and will be subject to moderation based on the "top 20%" clause mentioned below.
* After Hours User Policy NEW!
◦10 Day Rolling WIndow - If you're in Top 20% of IS users for this connection speed, you will be shaped
◦User Policy applies to After Hours (8PM - 8AM), Weekends & Public Holidays
* Daytime User Policy
◦10 Day Rolling WIndow - This account is Unshaped until you are rate limited by IS (see Daytime User Policy Table)
◦User Policy applies to Weekdays (8AM - 8PM)
◦After hours usage applies to 10 day rolling window"