Synthetix Staking contract epochs lifecycle - solidity

Question

I am trying to understand how to make a staking contract that blocks funds for a period of time and give rewards in epochs for the period that the funds are locked. I understand that synthetix contract is a very good starting point, but I have some trouble with understanding how their epochs works
How the Synthetix Staking Contract starts a new epoch? From what I am seeing, they have a function notifyRewardAmount which seems to add a reward duration and an amount for that period. But how they call this function with precision on each end of a period?
function notifyRewardAmount(uint256 reward) external onlyRewardsDistribution updateReward(address(0)) {
if (block.timestamp >= periodFinish) {
rewardRate = reward.div(rewardsDuration);
} else {
uint256 remaining = periodFinish.sub(block.timestamp);
uint256 leftover = remaining.mul(rewardRate);
rewardRate = reward.add(leftover).div(rewardsDuration);
}
// Ensure the provided reward amount is not more than the balance in the contract.
// This keeps the reward rate in the right range, preventing overflows due to
// very high values of rewardRate in the earned and rewardsPerToken functions;
// Reward + leftover must be less than 2^256 / 10^18 to avoid overflow.
uint balance = rewardsToken.balanceOf(address(this));
require(rewardRate <= balance.div(rewardsDuration), "Provided reward too high");
lastUpdateTime = block.timestamp;
periodFinish = block.timestamp.add(rewardsDuration);
emit RewardAdded(reward);
}
I believe that they are using some sort of a script, but this is a single point of failure and sounds like it's a bad idea to do