The phrase "presumptive ceiling" refers to an assumed or estimated maximum limit. It means the highest point or boundary that is anticipated or presumed in a particular situation. Full definition
Justice O'Marra irrefutably stated there should be a reduced presumptive ceiling of 12 months for youth cases that are non-complex cases. (criminallawoshawa.com)
once presumptive ceiling is exceeded, burden shifts to Crown to rebut presumption on basis of exceptional circumstances; exceptional circumstances outside the Crown's control: (1) reasonably unforeseen or reasonably unavoidable, (2) can not reasonably be remedied; if exceptional circumstance relates to a discrete event, delay reasonably attributable is subtracted; if exceptional circumstance arises from case's complexity, the delay is reasonable. (slaw.ca)
below presumptive ceiling, in clear cases, defence can show delay is unreasonable; to do so, defence must establish: (1) it took meaningful steps demonstrating sustained effort to expedite proceedings; (2) case took markedly longer than reasonably should. (slaw.ca)