The timelimit for multi is always worked out as number of cubes attempted multiplied by 10 minutes. Eg. 4 cubes = 40 minute limit, 12 cubes = 2 hour limit.
However, with the new rules, that still applies but if you go over 6 cubes your limit stays at one hour. Eg. 4 cubes = 40 minute limit, 12 cubes = 1 hour limit.