Replace datetime to unixtime on Apache error_log

I'm need create a script replace datetime to unixtime on error_log apache files

error_log:

[Mon Nov 01 21:48:54 2021] [:error] AH00898: Error reading from remote server returned by xxxxxxxxxx, referer

I need change it to:

[1635803334] [:error] AH00898: Error reading from remote server returned by xxxxxxxxxx, referer

I've a script which change unixtime to datetime with perl (I use it with squid log), any change to inverse logic here?

#! /usr/bin/perl -p s/^\d+.\d+/localtime $&/e;

This script change timestamp ONLY and preserves anything else on stdout/file, I need something like this.