My UK visa expires on January 28, 2018. Can I visit the UK from December 11, 2017 to January 5, 2018? Will I be turned away?
You can visit until the last day. That is what the validity dates are for!
Many countries give visas of a certain length to cover changes of plans but there is no reason that you can't use the entirety of the visa subject to the maximum duration per stay which is often shorter than the validity of the visa.