Hi Tsalsabilla !
Since you are using Text Area, its values would return the value which is of type cell array. But min function requires the data to be of type double. The easiest way would be to use Edit Field(numeric) to get the values and do the remaining stuff as you are doing. Edit Field(numeric) returns the value as type double. If you still want to use the Text Area and get it working, you can convert the data types of the values before you use it to plot.
For ex:
T1=str2double(char(app.BreakdownTime1.Value));
T2=str2double(char(app.BreakdownTime2.Value));
T3=str2double(char(app.BreakdownTime3.Value));
T4=str2double(char(app.BreakdownTime4.Value));
T5=str2double(char(app.BreakdownTime5.Value));
T=[T1 T2 T3 T4 T5];
plot(app.wbldist,wblplot(T));
