@echo off &SETLOCAL EnableDelayedExpansion
set "out="
FOR /F "tokens=*" %%L IN (hostname.txt) DO (
for /F "delims=" %%M in ('systeminfo /s %%L^|findstr /c:"System Boot Time" /c:"Host Name"') do set "out=!out! %%M"
)
echo %date% %time% - %out% > Result.txt
Previous Batch file create Result.txt file with one line! If you want separated lines for the date and time, replace last line by these ones:
(
echo %date% %time%
echo %out%
) > Result.txt