Each pool calc is most likely based off their "time to next block solved" data
I don't think that's how it works. All calculators function the same way (from all the pools and sites like WTM) and they don't use "time to next block solved" to estimate your profits. They just take the difficulty (current, or 24h avg, or whatever), calculate the odds of finding a block, and then divide the total reward proportionally to your hashrate. The "time to next block solved" is calculated with the same arguments: the pool just checks the current difficulty, and then, knowing the target TTF for the particular coin and the pool's total hashrate, it can estimate how many blocks it should find for a given period of time.
