It is not safe to rely on the system’s timezone

If you receive the error “It is not safe to rely on the system’s timezone” when installing WordPress, you need to modify the php.ini to include your timezone.

So open up php.ini and find the [Date] section. Add the following line:
date.timezone = Australia/Sydney
modified for your real timezone of course!
Now you must reboot your IIS server for the change to take effect. Conveniently, you can do this by typeing iisrestart at a command prompt.

You’ll probably find at this point that you can’t re-do the installation because WordPress tells you that the install is already complete. Open up phpMyAdmin, select your wp database. Click the Check All button then choose Drop from the drop-down list. Click Yes. Now you can reload the wp installer and it should proceed properly.