Getting Bitcoin's Block Number In A Specific Date And Hour?

I would like to know what is the Bitcoin block number in an existing date at an exact hour. for example what is the block number closest to 1.1.2017 at 00:00 UTC. What is the easiest way to do so?

Convert the time to seconds since the UNIX epoch:

$ date -ud "1/1/2017"
Sun Jan 1 00:00:00 UTC 2017
$ date -ud "1/1/2017" +%s
1483228800

You can also use Epoch Converter to convert it.

Add three zeroes to that number and append it to a blockchain.com URL:

https://www.blockchain.com/btc/blocks/1483228800000

And there you have it:

446033 (Main Chain) 2017-01-01 00:02:33

And if you want the previous block, clock on the previous button and scroll to the end:

446032 (Main Chain) 2016-12-31 23:44:04

So block 446,032 was mined at 12/31/2016 at 23:44:04 UTC and block 446,033 was mined at two minutes and 33 seconds after midnight.