As far as I know Windows 8 desktop only runs in 32 bit as a general rule. I can make a 64-bit version BSLoader. (BearShare 5 only runs in 32-bit mode AFAIK.) Some apps like Internet Explorer have the option to run in 64-bit.
Vital for Windows 8 is for the BSLoader to be set to Run as Admin. else it will not revert the date as you discovered.

Find the BSLoader in your programs folder and get Properties, Compatibility tab, check option to Run this program as an administrator. Tell me if this fixes the problem.
If you don't have immediate access to the program folder, then open the Run utility, copy-paste in:
%ProgramFiles(x86)%\BearShare Test

It is no surprise BSLoader brings up alarm bells in your security software. I suggest to give it an exception rule in your security software which is usually possible. BSLoader is based on batch scripting which most security software will treat highly suspiciously.

I was not aware BearStart would run in Windows 8, it did not work for me.

And yeah I never figured out how to include an error code to 'force' BSLoader to quit if it could not complete the reverting of date stage. I could re-look at the code to see if I can incorporate error code to run as smoothly as some other error code does in the same script. The force quit command I used is after BSLoader completes its tasks as an insurance for closing properly.

Edit: hour later: My testing of a new BSLoader with 8 second delay with an appropriate error handling without Admin privileges seems to work as hoped on Win 8. Seems to also work in Win 7, although it was able to find BS despite not being in the program folder. Seems to work in XP despite not being able to find BS to launch when BSLoader was not in the program folder. My original efforts a month or two ago at this kind of error handling did not work, so perhaps I've finally got it right.
So this even newer (lol) BSLoader was able to change date and revert back without admin permissions. But I cannot guarantee it will work that way for everyone. The test results might have been conflicted by already having BSLoader on the system. Though trashing the file and running the new BSLoader seemed to work fine even though it was not set to run as admin.