get local time from UTC refered dataset

I want to make a daily sum for a local calender day with 3-hourly data in UTC Greenwich time. The filename contain the date and time in this format yyyymmdd.hh To get a Greenwich calender day I have done this (in MATLAB):

C = zeros(8,6,NumOfDates);
for i=1:NumOfDates % number of dates
 B = zeros(8,6);
  for j = 1:8 % 24h/3h interval, number of hour data within 24 h for 3 hourly measurement
   A(j)= xxxxx % not specified here as it is irrelevant for the question        
   B = B + A(j);
  end
  C(i)= B; 
end

Can I do following to get local time? (here 18 UTC previous day to 18 UTC next day)

C = zeros(8,6,NumOfDates-1); % initialise daily 3h-derived data collection array
for i = 1:NumOfDates-1 % date-lopp
%.....
    B = zeros(8,6); % Initialise for every day
    for j = 1:4 % hour-loop
        hour=0:3:15;
        %.....
                A(:,:,j)=3*prec(MatrixN:MatrixS,MatrixW:MatrixE); % area extract, 3-hourly to hourly by assuming same 
        end
        B(:,:) = B + A(:,:,j); % sum hourly data into daily for extracted area
    end
    C(:,:,i)= B; % collect daily 3-h derived values

F = zeros(8,6,NumOfDates-1);
for k = 2:NumOfDates % date-lopp
%.....
    B = zeros(8,6); % Initialise for every day
    for j = 1:2 % hour-loop
        hour=18:3:21;
                A(:,:,j)=3*prec(MatrixN:MatrixS,MatrixW:MatrixE); % area extract, 3-hourly to hourly by assuming same rain rate the next 3-h
                TimeVector(count,:)=strcat(Datename,hour);
        end
        B(:,:) = B + A(:,:,j); % sum hourly data into daily for extracted area
    end
    F(:,:,k)= B; % collect daily 3-h derived values
   end
   Y = C+F;