I'm using NiceHash Miner with GPU and Dagger Hashimoto algorithm. It shows estimate of 1,35117 mBTC/day which is equal to 0,05629 mBTC/hour. After an hour I've checked my balance increase and it was only about 23% of 0,05629 mBTC/hour. Why there is such large mismatch between these values?
Because estimated balances on the miner are, estimates.
Balance is actual earnings.
Balance estimates change every few seconds in real time based upon active bids on whatever coin you are mining.