4 to 6 weeks for a fishless cycle is typical. Can take longer though, every cycle us different.
A few questions and a few points to raise.
- How have you got your ammonia upto 8ppm? Dosing ammonia? Fish food?
- Have you done anything to seed the filter? Best method is introducing some filter media from an established filter (perhaps you have a friend that keeps fish). Next best option would be a biological booster like Dr Tims One + only or seachem stability. If you dont do anything to seed the filter your 4 to 6 weeks will be more like 3 months.
- 8ppm of ammonia is way too high. Concentrations above 6ppm is generally accepted will kill off any beneficial bacteria. 4ppm is a more normal concentration to start off a fishless cycle. 50% water change is needed to bring that level down.
This is the guide to fishless cycle that people are normally pointed to.