Bitcoin halving occurs when 210,000 blocks have been mined successfully and when it happens the rewards per block are reduced to half. There is no fixed date of it and all those sites have just predicted that when the 210,000 blocks are going to be mined. I recommend you to not rely on that information, but wait for the event to occur.

The Bitcoin halving is going to take place at block no 840,000, and currently 792,936 block no is mined so it's still far to reach the no 840,000 for halving to happen. The halving is going to take place and no one can stop it but it's not going to take place on an exact date and that's why I recommend you to wait for it rather than relying on the information available on those websites.

The reason behind the difference might be because of two things one is "Block Time Variance' and the other "Network Hash Rate." The average time to mine a block should be approximately 10 minutes but sometimes it varies by seconds and that causes mistiming in calculations. The time variance happens because of Network hash rate and it sometime increases and sometime decreases depending upon the mining activity of the miners on the network. When the hash rate fluctuations happens consistently, the block time will be affected by that. That's why it's not possible to predict the exact date or time of the halving event. However, it's a confirm thing that Bitcoin halving will take place anywhere between March to June of the year 2024, and still it can vary a little bit.