I have some code here for an important time within my organization that texts clients their appointment times. I noticed an issue that when someone books ahead of daylight savings time, it does not tell them the correct time, it is still an hour behind. I am currently looking for a solution by implementing a formula that accounts for DST but I have not been able to implement a good solution as of yet. 

Here is the formula that displays the correct time for our timezone 

This is called Appointment_Time__c

IF( OR( VALUE( MID( TEXT( Start_Time__c - (6/24) ), 12, 2 ) ) = 0, VALUE( MID( TEXT( Start_Time__c - (6/24) ), 12, 2 ) ) = 12 ), "12", TEXT( VALUE( MID( TEXT( Start_Time__c - (6/24) ), 12, 2 ) ) - IF( VALUE( MID( TEXT( Start_Time__c - (6/24) ), 12, 2 ) ) < 12, 0, 12 ) ) ) & ":" & MID( TEXT( Start_Time__c - (6/24) ), 15, 2 ) & " " & IF( VALUE( MID( TEXT( Start_Time__c - (6/24) ), 12, 2 ) ) < 12, "AM", "PM" )

And then I have another formula that does the same thing as the first one but it is an hour ahead. 

This is called Appointment_Time_DST__c

IF( OR( VALUE( MID( TEXT( Start_Time__c - (5/24) ), 12, 2 ) ) = 0, VALUE( MID( TEXT( Start_Time__c - (5/24) ), 12, 2 ) ) = 12 ), "12", TEXT( VALUE( MID( TEXT( Start_Time__c - (5/24) ), 12, 2 ) ) - IF( VALUE( MID( TEXT( Start_Time__c - (5/24) ), 12, 2 ) ) < 12, 0, 12 ) ) ) & ":" & MID( TEXT( Start_Time__c - (5/24) ), 15, 2 ) & " " & IF( VALUE( MID( TEXT( Start_Time__c - (5/24) ), 12, 2 ) ) < 12, "AM", "PM" )

And then finally, I have a formula that determines the date and then it converts the normal time into DST, here is that formula that I have not been able to correctly implement because it does not convert correctly when it should. 
 

IF(OR(AND(DAY(TODAY()) >=10 , MONTH(TODAY()) >= 3), 
AND(DAY(TODAY()) <=3 , MONTH(TODAY()) <=11)) , 
Appointment_Time__c , Appointment_Time_DST__c)

Any help on what I am doing wrong would be greatly appreciated, 

Thanks in advance.