It would be best to read it using readtable.
Assuming that you did not do that and read it in as a matrix, this may do what you want:
M = [2005 5 20 17 140 3353 35.3 7.7 18 17.6 826 0 2.6 211 0 705 116 589 60 37.8 98.5
2005 5 20 18 140 3354 35.7 7.6 18 17.7 826 0 2 121 0 446 90 356 60 24.2 102.5
2005 5 20 19 140 3355 34 7.9 20 17.3 826 0 2.6 187 0 178 62 117 58 10.7 107.2
2005 5 20 20 140 3356 32.1 8.7 23 17.1 826 0 3.2 168 1 1 1 0 10 0 112.3
2005 5 20 21 140 3357 30.8 10.6 29 17.5 826 0 1.2 227 1 0 0 0 0 0 119.1
2005 5 20 22 140 3358 29.5 10.6 31 17.1 826 0 0.8 218 1 0 0 0 0 0 127.4
2005 5 20 23 140 3359 28.2 10.3 33 16.6 826 0 0.8 261 1 0 0 0 0 0 139.1
2005 5 20 24 140 3360 26.9 10.3 35 16.2 826 0 0.6 148 2 0 0 0 0 0 154.5
2005 5 21 1 141 3361 25 9.9 38 15.3 826 0 0.8 176 2 0 0 0 0 0 -174.3
2005 5 21 2 141 3362 23.1 9.7 43 14.6 826 0 1.3 223 2 0 0 0 0 0 -164.4
2005 5 21 3 141 3363 21 9.1 46 13.5 825 0 1.3 248 3 0 0 0 0 0 -146.5
2005 5 21 4 141 3364 20 10.6 55 14 825 0 2.4 214 3 0 0 0 0 0 -133.2
2005 5 21 5 141 3365 19 11 60 13.9 825 0 1.5 218 3 0 0 0 0 0 -123.2
2005 5 21 6 141 3366 18.3 11.4 64 13.8 825 0 2.4 282 3 0 0 0 0 0 -115.6
2005 5 21 7 141 3367 18.6 11.4 63 14 825 0 1.7 246 4 16 16 0 3 3.9 -110.1
2005 5 21 8 141 3368 21.5 11.3 52 14.9 825 0 1.3 278 4 270 125 146 55 17.2 -105.2
2005 5 21 9 141 3369 24.4 11.9 46 16.2 825 0 1.5 288 0 516 55 461 60 30.7 -101.1
2005 5 21 10 141 3370 27 9.8 34 16 825 0 2.2 222 0 739 73 666 60 44.5 -97.1
2005 5 21 11 141 3371 29.3 9.1 28 16.4 825 0 1 240 0 913 93 820 60 58.4 -93.1
2005 5 21 12 141 3372 31.3 8.9 25 16.9 825 0 1.7 216 0 1027 109 918 60 72.3 -87.5
2005 5 21 13 141 3373 32.8 8.7 23 17.3 825 0 1.3 173 0 1078 127 950 60 86 -65.2];
T1 = array2table(M); % Create Table From MAtrix
DT = table(datetime([M(:,1:4), zeros(size(T1,1),2)])); % Create ‘datetime’ Table
T2 = [DT, T1(:,7:end)]; % Horizontally Concatenate
TT = table2timetable(T2); % Convert To ‘datetime’
Now, you should be able to do what you want with the timetable, ‘TT’.
