12 weeks seems like a bad idea. I would be hurting if I got put on a 12-week schedule. I'm currently on an 8-week schedule, and my symptoms (mostly pain) often start to return after week 6. They get knocked back with the new injection 2 weeks later. I'd be in bad shape if I had to to wait an additional 4 weeks before getting the next dose.
In the US it is common for Stelara dosing to to get cut to 4 weeks, depending on how effective the standard 8-week schedule is. 12 weeks would a step in the opposite direction. In the US Stelara is FDA approved for 12 week dosing for psoriasis but not for Crohn's.