I had always heard that LiveCD mode leaves nothing behind, and makes no changes to the PC. I recently discovered that use of Linux Mint in LiveCD mode is changing the time clock on my PC by about five hours. Are there any other changes a LiveCD is capable of?

I had planned to have MX Linux installed to my secondary (SSD) drive. Will messing with the time clock across the board continue? Can it reach into my primary HDD, and affect my Win 7?

I'd say not unless you mount that drive as rw

Changing the hwclock is a BIOS call.

Granted a live CD used intentionally a certain way can modify you other partitions, in fact that's one of the reasons for live booting is to fix something broken.

By “time clock on my PC,” do you mean the hardware clock? Does the time stay changed when you reboot to Windows?

If not, perhaps the CD is configured for the wrong time zone. You probably can’t fix that on the CD, but you should be able to change the time zone while running the live CD.

You would be able fix it on the installation to your SSD.

What timezone is it changing it to?

Where are you located, what timezone? My first inclination is that it is not changing the time at all but is simply displaying UTC rather than local time.

There is some setting to fix that time issue but you'd have to remaster the live something like cd.timedatectl set-local-rtc 1 --adjust-system-clock.

At one time almost no live media mounted local drives. Some now will by a simple click or even automount.

I just tried MX 19.2 live in a VirtualBox virtual machine. As a frame of reference VB hwclock defaults to UTC and the live timezone defaults to EDT. Looking at the shutdown messages it does not set the hardware clock.

So I assume you are just referring to the desktop time which is probably off if you don't live in US on the east coast. Other live CD could be configured differently.

If you reboot back to Windows is the time off by 5 hours?

I see you were running Mint. Standby for an update...
Mint defaults to UTC time zone. The shutdown messages were much faster then MX and I could not say if the live version actually updated the hardware clock when shutdown.