Edit: Whe i see the transaction history i understand why my earnings is so slow, but i dont understand why.
When your proofs of work are accepted by the server they are registered in the current (not yet finished) shift. Each time a block is found the last 10 completed shifts are paid.
After the shift is completed the work is now eligible for pay from any blocks we find. From then on, every time we find a block those proofs of work are paid from the income in that block, until 10 more shifts are completed. This causes a delay from the moment you do the work until it is fully paid and stops receiving payments.
Currently shifts take almost 1 hour. So it takes anything from a split second to 1 hour from the time you do some work until its shift is finished. And then it takes 10 shifts (10 hours) until it is fully paid. So the delay from you did some work until it is fully paid is 10 to 11 hours with the current pool hashrate and Bitcoin difficulty.
In addition, if you don't have the prepay perk activated then the payments are only set up when a block is found but not executed until the block is confirmed. This causes an additional delay of about 20 hours from the block is found until the coins hit your BitMinter account.
That's a total payment delay from 10 up to 31 hours.
And then there is luck... daily earnings fluctuate as we play the Bitcoin lottery called mining.