function _estimateCreditAccrualTime( address _controlledToken,uint256 _principal,uint256 _interest ) internal view returns (uint256 durationSeconds)  {
  uint256 accruedPerSecond = FixedPoint.multiplyUintByMantissa(_principal, _tokenCreditPlans[_controlledToken].creditRateMantissa);
  if (accruedPerSecond == 0) {
    return 0;
  }
  return _interest.div(accruedPerSecond);
}
function _calculateTimelockDuration( address from, address controlledToken, uint256 amount) internal returns (uint256 durationSeconds, uint256 burnedCredit )  {
...
  uint256 duration = _estimateCreditAccrualTime(controlledToken, amount, exitFee);
  if (duration > maxTimelockDuration) {
    duration = maxTimelockDuration;
  }
  return (duration, _burnedCredit);
}
