My guess is you can cancel after 6 months if you want to. It's a promo for new TMN customers, who haven't had the package in the last 120 days according to this thread in the Bell Satellite forum.
If your plan is to just keep it for 6 months and cancel, keep in mind that Bell says it might take 6-8 weeks to apply your 50% credit.
Like all promos, the strategy is you'll like the programs so much that you will pay full price after the promo. As an example, Super Channel has had promos with 3 months free and you could cancel within the 3 months and not pay a cent.
I subscribed online and there was no mention of having to sign up for 1 or 2 years. I had 2 months on my first bill with TMN and there was 1 months credit. I plan on cancelling around the 6 or 7th month but will stay until I receive all my credits probably.
FYI just noticed the forum I was in this was with Bell satellite not Fibe.
Called Fibe TV number today to ask about TMN offer; CSR confirmed it is 1st 6 months at 50% off, so $10 / mnth, and then regular price thereafter; no contract involved. i.e. you are not committing to any term for TMN
Ordered it; think for existing customers the promotion is on until 19-Jun, end of year for new customers.