(1) Method 1
for /f "tokens=2-4 delims=/ " %%a in ('Date /T') do set DateVar=%%c-%%a-%%b
for /f "tokens=1-3 delims=: " %%a in ('TIME /T') do set TimeVar=%%a:%%b:%%c
echo %DateVar%
echo %TimeVar%
To ensure 24 hour format for time, do a customisation of the Regional and Language Options
from Control Panel
(2) Method 2
@echo off
for /f "tokens=1-2 delims=." %%a in ('echo %time%') do set TimeA=%%a& set hsec=%%b
for /f "tokens=1-3 delims=:" %%a in ('echo %TimeA%') do set hh=%%a& set mm=%%b& set ss=%%c
echo %hh%%mm%%ss%%hsec%
(3) Method 3
for /f %%a in ('powershell -Command "Get-Date -format yyyyMMdd_HHmmss"') do set datetime=%%a
ECHO %datetime%