I agree with you on the fact 60 seconds would be easier for the newer players to understand as it is 1 minute, but I think that it should be 50 seconds so that it can stay within that time frame of 1 minecraft hour.
Since I have no guess as to how big the map is, I can't really say whether you should be able to escape the section when it is active. If it is a smallish map (SG4 or Breeze Island size) then I think it's fine to have the barriers preventing escape. But if it's on a much larger scale like the first survival games, then the barriers shouldn't be in place because the arena is big enough it would take a seriously long time to get out of the section.