I don't think five years is inappropriate. I've learned that it does take time to do these things in government, even though we would always like things to happen perhaps faster than it would seem to take. I think it's important to give a reasonable timeline, but with clear milestones along the way, in order to make sure the project doesn't slip and then become a seven-year or ten-year one.
And there will be changes. Just because of the cycle of budgeting and the presentation of votes, there is a certain delay. Even if you started today, it would probably take two years to put it in. So five years would seem to be reasonable.