PHP+JS countdown a few seconds and then not move. Workaround

PHP+JS countdown a few seconds and then not move.
There were two problems with a countdown code.
1. The countdown is quite smooth after the refresh but wait a half minute, the countdown starts the card and then does not move, this is why?
2. After the card is refreshed, the webpage does not respond, unless you turn off the page and reopen it, and then repeat the first question.

The code is as follows:

PHP Code

------Solution--------------------
I've done something like this before, as if I could search for it.

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