System Time and file time

Hi,

My server is in Canada and I'm in Brasil. So using Webmin > Hardware > System Time, I have made a change in the Time Zone and set it to Sao Paolo. Now, on the System Information page, the value of "Time on system" is correct. But i've a CRON for backuping my MariaDB tables. And when I look at the time of the file on disk, I see it don't have the right time, but in fact it had the "old time".

Don't undertstand why, and if rebooting, it's still the same.

How can I "link" the change made under Webmin with the time used for the files?

Best regards PL