With the allowance to change the portfolio once a year, there is plenty of opportunity to plan when to transition from equities to bonds...if ever.
I approach this a little different. If the investor will be contributing enough money to cover college costs (at a presumed rate of return say 8%) then never transition the money to bonds and use the account remainder as a legacy.
If the investor is expecting to contribute funds to cover partial college costs (i.e. inveitable liquidation of the account) then beware of equities inside of 5 years.