I just got my UK Standard Visitor visa, valid March 14-Sep14 2019. In my application, I intended to travel on May 23 - June 5, 2019. Can I still change my travel dates to earlier dates than my application?
Travel plans change all the time. You are good to travel anytime on or after 14 March, providing you exit on or before 15 September. Just a note of caution against extending your stay significantly beyond the length of time originally stated in your application Cancelled UK visa on entry