SMTs are UIA (User Issued Assets) so they are issued only once, and the generation mechanism will be locked in at issuance. After the ICO, new tokens can be issued only by inflation. And, AFAIK, the inflation will be in sync with STEEM generation blocks. If an SMT must generate 1 token per minute, then this will be calculated based on STEEM generation (every 20th STEEM block will issue also an SMT).

At least that's what I understand from the White Paper.